Overloaded By Tech: The Case for Simplicity
It is tempting to purchase new devices, equipment and kit to track a number of performance metrics and to improve athleticism and to include these into a training schedule to monitor training or performance over time, or used as a tool for feedback of training effectiveness, as well as the latest bike or shoe or equipment to achieve 'marginal gains'. Chasing power and pace in each workout can lead to stress, injury. Probably, most people will find bigger gains by developing the aerobic engine.
A recreationally active individual typical of the general population engaged in health and fitness, defined as 'participating less than or equal to twice a week in aerobic activity for a total of 80 minutes at moderate intensity' (ACSM, 2006) can make larger performance gains with simple lifestyle interventions that improve underlying metabolic health, by reducing carbohydrate intake to increase fat oxidation rates (Volek et al., 2016). The basis to training for many, should be an individual focus on metabolic health, which drives energy production, to later improve aerobic function, strength, performance, recovery and adherence with improved overall health.

Unless eking out the final performance improvements, for most, expensive equipment is nice, probably not required.
Technology
Training by heart rate became a popular method for training when the heart rate monitor was first developed (Säynäjäkangas, 1977), which has since been superseded as technological developments have allowed increased access to collection of complex physiological performance metrics. These are useful when used appropriately for peak performance at an elite or sub-elite level. However, for most, understanding the physiological processes that occur with activity, and the adaptations to exercise, will mean heart rate training is of greater benefit in the longer term, to reduce injury risk, maintain engagement and improve performance.
Heart Rate Training: Finding Your 'Gears'
Heart rate training is underrated, and, particularly for endurance sports, should be the basis to training. By training to heart rate you can find the underlying aerobic condition of the body for that mode of exercise, and develop it appropriately by using the MAF formula: 180-AGE (Maffetone and Laursen, 2020) most importantly, with the lowest risk of injury and greatest rate of recovery to allow for an increase in volume. Increasing the time at a lower heart rate improves aerobic capacity and mitochondrial function.
Training by heart rate is individual, and tells you more accurately than pace or power metrics, which substrate you are predominantly oxidising for energy. Once these gears, or zones, are identified, you can fuel workouts appropriately, develop the aerobic 'engine' and consider applications of HIIT for performance. Heart Rate Variance can also monitor underlying 'stress' from all areas of life, such as alcohol, illness, injury and disease.

Keep it simple: Train by Feel, Track Heart Rate, Heart Rate Variance (HRV) and Time.
Proprioception: Feel and Focus
This is the ability of the brain to detect the body's position in space, much like an intrinsic awareness system. Proprioception relies on populations of mechanosensory neurons distributed throughout the body, which are collectively referred to as proprioceptors (Tuthill et al., 2018) and was traditionally thought of as a 'muscle sense' for the body to control motor commands. It is a vital aspect of motor control for everyday activities, and when degraded or lost, can have a profound impact on function in diverse clinical populations (Hillier et al., 2015). Proprioception can also be impaired in gradual-onset musculoskeletal pain disorders and following trauma (Clark et al., 2015).
Training by Feel
Being aware of the body and how it responds to physical activity and training can be individual, and this requires proprioception. The great Arnold Schwarzenegger was an advocate of 'putting the brain in the muscle' to recognise muscle failure when bodybuilding. Other techniques can include closing eyes to enhance awareness during a 'stork stand' for balance, and kinesthetic tape following injury. Exercise enhances proprioception and the ability of the body to send messages to the brain. By focusing on developing proprioception rather than a specific pace or time, you can individualise your training.

How it was done for a very long time, in different and harsh environments, for survival.
So what?
If you are currently always training to a fixed performance metric such as pace or power, make a change by tracking heart rate to find your 'gears' you are training in, train those gears for your specific goal. Heart rate variability (HRV) to measure cumulative recovery, and train by time to observe how the body feels.
Take home:
Developing proprioception, or the ability to 'put the brain in the muscle' develops the mind-muscle connection, and improves awareness of one's body in space, important as we age and for injury recovery and prevention, but also for pushing the envelope. This is useful in developing feel, to reduce risk of injury and increase performance.
Check out the great MAF: https://philmaffetone.com/
References
Clark, N. C., Röijezon, U., & Treleaven, J. (2015). Proprioception in musculoskeletal rehabilitation. Part 2: Clinical assessment and intervention. Manual Therapy, 20(3), 378–387.
Hillier, S., Immink, M., & Thewlis, D. (2015). Assessing Proprioception: A Systematic Review of Possibilities. Neurorehabilitation and neural repair, 29(10), 933–949.
Maffetone, P., Laursen, P.B. (2020). Maximum Aerobic Function: Clinical Relevance, Physiological Underpinnings, and Practical Application. Front. Physiol, 11, 296.
Tuthill, J. C., & Azim, E. (2018). Proprioception. Current biology : CB, 28(5), R194–R203.
Volek, J. S., Freidenreich, D. J., Saenz, C., Kunces, L. J., Creighton, B. C., Bartley, J. M., Davitt, P. M., Munoz, C. X., Anderson, J. M., Maresh, C. M., Lee, E. C., Schuenke, M. D., Aerni, G., Kraemer, W. J., & Phinney, S. D. (2016). Metabolic characteristics of keto-adapted ultra-endurance runners. Metabolism: clinical and experimental, 65(3), 100–110.
Whaley, M. H., Brubaker, P. H., Otto, R. M., & Armstrong, L. E. (2006). ACSM's guidelines for exercise testing and prescription. Philadelphia, Pa: Lippincott Williams & Wilkins.