Is it the sound he liked of the exoskeleton clicking and cracking when he hit it? My cat likes this kind of sound as well and I've given him crumpled up tinfoil balls before (bigger than his mouth) and they make a nice satisfying sound. I've also put ping pong balls in the bathtub at night in...
He's a pretty laid back and chill dude, always up for a cuddle or two. He'll let you do just about anything to him and is very food and attention motivated, which makes training him a cinch!
Your cats are cute and fluffy! I've been taking my cat for walks too, but he seems to prefer walking on along a path and doesn't get as distracted as when I "free walk" him in the grass.
I own a very similar floor-to-ceiling 3 tier cat perch, just be prepared to replace carpet panels and wrap sisal rope around damaged parts. It's by far the best investment I've made for my cat (only $40~!!) and he runs up it multiple times a day like a squirrel and perches at the top and looks...
I bought a knock-off furminator called the Shed ender and it works really well! I do short and quick bursts of brushing to get the most fur off him and he loves it. He rolls, purrs and even lets me do his white tummy, lol! He never wanted his tummy touched before, and now I can be very thorough...
For grooming my shorthair, I found that the "shed ender" type comb works really well. I get a lot of compliments on his coat when I take him on his harness outside my condo. Also combined with Wellness wet food and lots and lots of love :)