IMO overpriced and not all that practical.
You're tied to their cogs that only go down to 13t (up to you whether you'd use a 12t) and they only do fixed or fixed/free. You can't borrow standard cogs (although if you have the double sided version you could use the free side but no lockring).
I have fixed/fixed training wheels and rarely change cogs, just flip the wheel in a session. I'll change the cogs periodically depending on where I'm at with training, but for single sessions, I only really use the 2 cogs. I purchased the similar Miche system for my daughter's track bike and I really don't know why as it was just a waste of money IMO as with her being a junior, she's on fixed gears so they don't change and the adapter+cog+lockring cost more than 4 decent quality cogs.