Many thanks, folks. Reliability was my #1 concern. If it doesn't feed, it's just for show, and that I don't need.
There are 51 reviews on Brownells with 6 1-star ratings and 1 2-star. One of the best 5-star reviews was by 22-year military guy, user "Redrumu," who shows his drum mounted on--ta dah!--another Tavor!
One reviewer who gave it 1 star said, "The pin at the top right shifted after the first sixty rounds. The drum could not be released without removing a takedown pin to gain access to the top of the drum." Another had a similar experience: "Retaining pin on right side of the feed tower partially backed out during use. The magazine would not drop out of the magazine well and could not be pulled out. I had to remove my upper, use a pin punch and reinstall the pin to remove the magazine from my rifle." The other poor ratings all had to do with difficulty charging the mag (which doesn't really concern me; it's not as if I'd ever anticipate having to do a hurry-up "battlefield" refresh) and secondarily the weight (but...isn't that expected?).
I've been extremely happy with the PMAG 40-rounders for a little extra capacity; have a number of these. But the downside to those is the length. In tight interior conditions and having to rotate the angle of the rifle, I fully expect that under stress I might be bumping it into walls or doors. The D-60 is a honking lot wider, but it appears to be the same length from the mag well as a 30-rounder. I'm thinking the width may be less of an issue than the length in the overall usability profile when getting through doors. But I could be wrong.
Anyway, if no one else here has had repeated reliability issues like the "retaining pin on right side of the feed tower," I think I'll order a couple later today.