Okay; based on my experience with these, and flats in general....
- No. Other than being flatwounds, they aren't very similar at all. I'd say that the Fender 9050L's are dead in the middle of the "modern, mid-focused flats, and will work, at minimum, pretty well for anything you want to play. The
tension (pounds of pull needed to bring them to pitch) is about average for flats of their gauge. Their
stiffness is also about average for flats; they work quite well with a pick, but are decent for finger playing as well. They're what I call "goldilocks flats"; not too anything, really; they're "just right"... I've had them on 4 basses, and currently have them on 2. I like them a lot... As for the Rotos? I've always used the heavier RM77LDs, but don't have them on anything at the moment. Had a BEAD set on a Carvin LB-20 for years, but took them off last year. Not because of the strings, though; I just couldn't justify the BEAD tuning. I also had them on an '18 Gibson Thunderbird for a couple of years. I really likes the strings, but the bass annoyed me - so I sold it a few months ago. The RM77s are just about the highest tension flats around (214.4 lbs.), and they are very stiff. The SM77's, OTOH, have a more reasonable tension (176.8 lbs.). They will still feel stiff, though; that seems to be a Rotosound trademark. As for the tone? I'd put their tone at the transition point between Old School, thumpy flats and the modern, mid-range flats. Either the thumpiest of the middy flats, or the most middy of the Old School flats. So, kind of useful for several genres, but not nearly as useful as the Fenders...
- Worth the price? That's really up to you. If you want fairly high tension, stiff flats with a serious bottom end, along with some low-mids and a touch of mids? Then, yeah, the SM77s will be worth the price. If you want some fairly flexible flats, with decent lows; lots of low-mids and mids, and some useful highs, then save your $$'s and get the Fenders...