From what I've seen, radiant heat panels are relatively uncommon in the UK, but CHE's inside protective cages like the one you have seem to be common. Guards like that seem to be pretty uncommon in the USA, but RHP's are easy to get. I have no personal experience with CHE's inside those guards, but I have seen them in enough photos of enclosures from the UK (in some cases with the snakes in the picture attempting to climb around on them) that they seem to be a safe solution if done right.

For what it's worth, the benefit of a CHE inside a cage like that instead of in a fixture shining through a hole in the top is that more of the heat will stay inside instead of escaping through that hole and around the rest of the fixture; same with humidity. A radiant heat panel is an efficient heating device because less of the heat it makes escapes the cage than a lamp on a stand resting on top.

So I would do two things. First is, look for some advice from UK people since they're more familiar with that method. Second, put the lamp in the wire guard and turn it on full blast for awhile and see how hot the guard actually gets. If it doesn't burn you, it won't burn your snake. Note that the reason this isn't necessarily true of a UTH that you just touch with your hand is that momentary contact is not the same thing as spending a long period of time sitting on top of something, and your snake can't sit on top of things that are mounted to the ceiling.