Alright, so protecting the shin is generally done to reduce actual phyiscal pain, which... what I would say is you REALLY want a full shin + instep protector. The most common injuries in kicking are when your opponent backs up or you trip or lose balance or slip or whatever... And you end up kicking with your foot... Which at the end is just a bunch of tiny ass breakable bones like your hand.
So really in MMA or Muay Thai you should be looking for a combination shin and in-step protector. You can get a cheap one that will do a fine job.
I have the venum elite standup shinguards. they're ~$100.
They work fantastic but are a little bit expensive. If i'm honest I feel like the premium money I spent probably wasn't worth it? I've tried other cheaper variants that all work fine. The BIGGEST thing you'll want is just a strap / fitting mechanism that is comfortable and doesn't slip. And that's going to change from person to person. But the levels of protection are basically all the same, it will absorb enough impact so that you won't break your foot or hurt the fuck out of your shin. Even $20 shin / instep protectors will probably protect you shins. So then it's just a comfort, you don't want some that are overly bulky or will slide off / not fit comfortably.
If you want to just like... never go wrong, Venum, Hayabusa, Fairtex makes a mean shin / instep protector. Avoid everlast avoid the silly like... full length long compression sock looking shin/instep protectors... They can fit REALLY weird and they're the only type of protector that A. Arguably might not offer enough actual protection and B. Even though in theory the only reason ON EARTH you'd ever wear a full giant compression sock looking protector would be so it fits snug, they can actually slide around a lot.
Or think of it this way, if those compression sock fitting guards really worked why doesn't Hayabusa / Venum / the actual top muay thai brands do them? Its's only a style of fitting you get in the cheap-o shit brands.