I haven't owned that one, but I did own a different lightweight Avaratec for a while. I appreciated how light and portable it was, but as such it was also very fragile. The casing was not a tough plastic, but rather kind of a kind flimsy one. So long as you're really careful with it, you should be okay. I, unfortunately, wasn't careful enough.
One issue I had was that it would crash during large file transfers, whether by network or by firewire. (The one I had didn't have a firewire port, but I used a PCMCIA adapter.) I never did identify the problem, but it's the only computer I've ever had that problem with.
I'm currently using an HP Compaq NC6220 which is about the same size and weight (probably a few ounces heavier), and it's much sturdier and reliable. It's not as powerful or feature-filled as the Avaratec you're looking at though, so a descendant of it may be more what you're looking for. (Ie, it doesn't have a DVD burner, not nearly as many media readers, and I am still without an included firewire port -- sigh.)
I have a tablet C3500. I can't say anything about the model you mentioned.
My tablet is light and works fairly well but I agree with bStro that there are better
models. The sound in these units are on the low end. Headphones a must.
My PCMCIA firewire works without any hitches. On my tablet I need to calibrate
the pen when doing drawings more often than I want to admit.