Let the hive mind of Engadget get that for you.
"I just switched to Sprint from Verizon about three months ago for the Pre. Then I went for the Hero about a week ago. Now, I miss my hardware keyboard and am thinking about switching to the Moment. I am still able to switch back to Verizon if I want and get the Droid when it arrives. Should I just trade up to the Moment when it comes out, see if I like it, and if not switch to the Droid? Or something else entirely? Help!"
Luckily I have a job where I can charge my phone if such a problem occurs. However this accessory although slightly bulky(Probably no way around it) actually doesn't look half bad. I'd probably have to se some user reviews before I forked over $100 for this though.