I bought 'em, I can't say I was terribly impressed after building two tanks. I suppose they couldn't hurt but, you know, I was really more interested in having tanks that didn't leak more than I was having the world's perfect RV. I used a LOT of ProSeal and there's a few rivets that are less than impressive.
Now maybe they'd be even less impressive with regular dies, but I don't know.
I know if I had it to do over again, I don't think I'd spend $40 for something I'm not going to use for, like, two weeks.
Maybe I'll sell you mine for $20.