I learned frontside slappies first in my late 20s. Felt amazing. I was inspired to learn them after joining a slappy session held at painted curbs beside an abandoned, bombed-out building covered in pieces, with a chocolate factory down the street, and that's where I spent many hours and learned them.
There was a small curb, and a big curb. The big curb definitely hurt to slam on, but felt amazing once I caught a slappy on them. I was fortunate enough to film some of them and threw them in video parts. I remember Koston saying in an old interview that lots of dudes couldn't do f/s slappies, so it felt like I'd reached a goal in skating where I could be considered good, haha. I mean I suck and always have, of course. People praised f/s slappies in interviews so like when I learned b/s tailslides, it felt like I'd reached a level to be a little bit proud of.
Backside didn't come as easy, which really infuriated me. I thought the opposite. It stayed like that for a long time where I'd lock into a willy grind constantly. Only in the last three years did I unlock them and can get my back truck on fully. And I never usually lock in and grind for a long time, it's more like getting the front truck on and off quickly while grinding the back truck for awhile, so by the time I come off, my body's twisted a little bit backside. It feels great.
The sad thing is though, I haven't done a frontside slappy in awhile because I started locking into weird f/s feebles which always pitch me and the slams started to make it feel like it wasn't worth it. I can still get into them but I haven't rolled away in a few years. Backside slappies have become much more fun and easy. But I want to do both f/s and b/s on a regular basis, that's a goal for the future.
I will say I'm not a fan of angled curbs. I like 90-degree curbs, it feels good to charge it and slappy into a straight curb. No judgement, though. And tech-slappy tricks, I never really got into that, I just prefer the basics.