Looking back
I used a tablet for about two years. I found the time savings on a day-to-day basis to be only nominal, because its so easy to key in field data to the software anyway. Sketching in the field with a tablet takes a bit longer than doing so by hand (in my experience), and regular sketching on a desktop is fast anyway.
The biggest time savings occurred when I got to a property too early, or due to scheduling problems, got stuck for a long period of time between two appointments. Being able to keep working instead of wasting your downtime in the field is a good feeling. The other residual luxury is the ability to pull an extra comparable from the field if needed, but this of course requires other hassles i.e. wi-fi access or your own direct access. I had Mcdonalds wi-fi, but it entailed actually finding a mcdonalds nearby, and possibly going inside the restaurant if the signal was not strong enough. I was close to connecting to the internet through my sprint cell phone, but when business went down, there really was no justification for the extra $40 or so per month it would have cost.
My machine weighed about 4.5 lbs and was about 13 inches wide, it was a bit too heavy and wide for my taste, so I would recommend something under three pounds, maybe 10 inches or so. Its hard to tell what will be comfortable from an online purchase or just by holding one in a best buy store.
Although my post is a bit negative, the technology itself is fun to play with, and you can brag about your device in your marketing materials i.e. ability to complete and send final inspections directly from the field. That too was a good feeling.
Hope this was helpful, best of luck,