When I, as a new rider, was finding out what bike fit worked for me (I am old and was very inflexible) I bought several cheapo stems of various lengths and angles. Once I found my correct position (which changed quite a bit over the first year), I bought a good one and sold the others on
eBay. I wasn't out of pocket by more than a few quid and even made a small profit on one of them.
PS I also did the same with saddles before I found what was comfy for me.
I now know to the exact cm what works for me and recently bought a new bike which was altered by my LBS to fit me perfectly.