The latch on some of these aftermarket battery covers doesn't always fit right, some will pop off repeatedly. Sometimes improves over time. When they work well, they're great.
I would also recommend when choosing a color that you pick one to match your original shell and don't try to get clever about it. I bought a blue cover thinking that the purple GBC I got from eBay looked a bit lighter/faded on the back, but I should've just gotten the purple, it was totally wrong. Luckily I also got a clear so I just used that one. I later replaced the shell with a FunnyPlaying one anyway, so no big deal. The teal cover I ordered for a teal GBC looks good to me and fits okay. If you're keeping the stock shell for some reason and you have a broken or missing battery cover, I think this is definitely worth picking up.

Works and looks good but is a little hard to get on

My cover was damaged in transit so I claimed it damaged through the route app. HHL approved and shipped one out immediately can’t thank them enough for their quick service! I also got a clear one that survived transit great replacement battery cover.

It fits well but the color is a little off.

It's not a 100% color match for a Grape colored GBC, but considering I have had it since '98 I cannot swear that the color hasn't changed somewhat anyway. It matches close enough that, unless you're super focused on detail like I am, you probably won't notice. Can't speak for the other colors, but for my money it does the job, and the fitment is a close enough match to my Atomic Purple GBC's door that I'm perfectly fine with it.

Fits well and is secure, color is pretty close (not perfect but you shouldn't expect that).