I have two and love them. As set out above, they hold more air than an AL, are slightly smaller and have better buoyancy characteristics - what's not to love? I'm not particularly concerned about the whole DOT issue dlndavid mentioned above, either (and you buying more of their tanks helps to insure they'll stay in business to keep the exemption alive, in any event).
As for the inserts, mine only had one insert. You take it out if you want DIN, you leave it in if you want yoke. I can't imagine what the other insert you're talking about could be for (or how you'd insert a different size adapter into the din plug).