Purchased the EyeCoach as a training supplement for my two children who are competitive juniors. It is an effective device for working on stroke production and muscle memory/repetition on rainy days, super hot days, or days when you just can't get to the courts. We get creative and work on a variety of common shots and contact heights, from waist height to head height contact points with the aid of a sturdy coffee table. In an larger open space both players can use it at the same time, with a player on each side alternating shots. We can also incorporate some footwork by having them move to the device from some distance.
Like all training devices of all other sports it cannot replace the "real thing" - the 'live' dynamics and decision making of live ball play. But is certainly useful for the areas mentioned above.
I would recommend having your coach watch you use it when you want to work on a specific shot, having someone record you using it for a few hits (then watching that recording, preferably with your coach, and making necessary adjustments), or take really good notes from your last lessons before you start. It's quite portable and you can bring it to your next lesson to ask your coach for tips.
Like any sport, you don't want to create muscle memory of an improper technique, that at best will slow your improvement and at worst can create a nagging injury.
I am a former NCAA D1 tennis player and can probably stay competitive with my kids for just a few more years 😉