I tried them years ago, and never got them to run well enough to be worth it. Also, when they had a malfunction it usually mangled the brass, rammed the bullet deep in the case, and generally caused issues. I will say I use them regularly in my Howa 300 blk bolt gun with a load of trail boss. It is really like a centerfire 22 at that point, but everyone that comes to the range with me loves to shoot it, so having a cheap bullet that gives both very low recoil and very low noise with a silencer is a big plus.
I will also say I completely forgot about the excellent speer bullets. I have had great luck with both the 125 grain TNT and the 130 grain HP bullets. I used to find them for a good deal on Midway, and Sportsman's usually had a good price (<$20/100) when they were in stock. I got really lucky and picked up a couple 250 bulk packs from midway a year or two ago for under .15/each and have been slowly working my way through those.