I am intrigued
My biggest caution is the controller part of it, the triggers and sticks.
I've had my fair share of controllers, and a sizeable chunk tend to develop issues with these components. Some after little use and some after mild use (that is to say playing excessive amounts of Rocket League). On a controller it's not too much of a hurdle. I feel alright opening that up to give some required maintenance of whatever sort I have laying around, but with a more expensive and advanced machine I'm not sure I'd feel quite so eager to engage in home-repair.
I could see myself forking over the cash, but I hope to see some information on replacement ease for these wear and tear parts. The machine won't last forever, but from my experience the computer bits won't be outdated before the controller bits will break - and that would suck.
For a Switch the controllers are separate entities - that doesn't seem to be the case with the Deck.
Also a note on the reservation fee - that fee counts towards the purchase price, so it's mostly there to ensure that you're serious about it and discourage fake reservations, as per the Deck FAQ:
"Does the reservation fee count towards my Steam Deck purchase price?