I haven't used it, but I wouldn't hesitate either.
When you consider that the fiberglass/epoxy sleve is not flexing, it should not be under alot of stress where it would be prone to cracking.
I've heard of people doing this with 5-minute epoxy, and I believe system 3 is a fairly reasonable quality resin.
I probably wouldn;t wanna use polyester resin, but any decent epoxy resin should be fine.
You could always test it by cutting a 1x2 of oak and splicing it back together with the socket system, then test to failure to see how strong it is. My guess is you'll be suprised and wont be able to break it without using a breaker bar or something for alot of leverage.