It's a interesting niche..
Most of us (myself included) just shorten the stock on cheap budget, but full sized PCP/CO2 guns (ratcatcher with a cut down stock (fitted with an adj buttbad) , and an AGS PCR1 with chopped butt both worked great for my kids for very little money).
..but if you don't want to mod your own.. then again, I think I'd be more tempted to buy a regular ultra and buy the junior sized stock for it, selling the stock on in due course.
whilst I get the logic behind lowering the power (around 7 FP ?), I think it's a problem for either HFT shooting, or when the shooter wants to move on, knowing that the gun must be sold.
Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.