I've used a bunch of them....
Here is my opinion on them, and it's just that. The RS150 and RS225 rock. Dual RS225's in a TMWW box just rocks crossed about 800-1000hz. The RS150 needs some attention in the xover region due to it double breakup mode. This must be dealt with agressively. The RS125--I didn't like it. The RS28-I didn't like it. I haven't tried the RS52 yet because the RS28 scared me off. Not that it's a bad tweeter. Actually, it's quite nice but I like a little twang in my tweet and there is no twang in this one. The RS series drivers are low distortion drivers and a great value for the money. Mate them up with a Seas tweeter like the 27TBFC or 27TDFC or 22TAF/G and you're good to go.
Paul