Interesting, but from what I read the 346xt does not have those easy buttons to get highway patrol and police, unless, is there a software program downloadable for the 346xt? Because you're right a handheld is so much easier to have and use I feel.
No the 346xt doesn't have the pre programming like the 15x, so you'll be giving up that option. I wanted to know what I was listening too and have full control, so the pre programming was only used the first few days I had the radio. I wouldn't recommend either radio if what you are looking for is plug and play. They both take a serious amount of time and effort to learn. There's plenty of help on here and other areas online, so the pain and suffering is short lived!.....
There are a number of software programs that work with the 15x and are interchangeable with the other Uniden DMA scanners, so there's no lack of support. FreeScan is the most often used and Free. ProScan ($50)is the most powerful and feature packed that I ended up buying after trying out 4-5 other programs.
To get the most out of your scanner it's almost mandatory you install and program it via software. You can certainly do it by hand, but so much easier via the computer. Both scanners have a huge amount of frequency space, so it's easy to drop in areas of interest if you travel quite a bit. I haven't had a chance to play with the GPS support yet, so that's next on my list.