What to consider when looking for a chainguard?
I bought 2 of these half chaincases: 

One of them is fitted to my wife's commuting mtb and does the job of keeping trouser legs and shoe laces out of the chain rings (with a guard disc fitted to the cranks as standard). I just couldn't get it to fit my hybrid without rubbing on the chain (and it was fiddly on the mtb). Both have 28-38-48 chain rings and i don't think it would fit anything bigger. 

I think the reason I couldn't get it on mine was the length of the chain run (it's an XL frame) possibly combined with the 11--32 tooth cassette. The shape of the crank arms might have something to do with it as well -- clearances are tight. You should consider ease of fitting/opening/removal for working on the chain, compared with how often you need access to the top of the chain run. You may find that it's more total effort than a clip or tucking your trouser leg into your sock every ride. 

There are similar chain guards out there. She's got an e-bike with one on. It looks like it would fit 2 chain rings but not 3 and has not branding on it.