I've run an Archos Gmini400 for about a year now as my backup/stealth deck. It's the same as the 402 in terms of audio, I think the 402 has some sort of upgraded video, but like you, I really don't care about that.
Yes, you can only go 1/8" analog line in through this adapter thingy. The internal ADC in it isn't really that bad, and compares with the internal in my D10ProII.
The recording levels are really great. Best I've seen yet. They are 16 segment total with 11 green, 3 yellow and 2 red. When you hit red you are just at clipping. You can adjust the levels (only both, no L and R seperate) wihle recording. The screen backlight is really nice and bright. Good for open situations, but not so nice for stealth. Good part for stealthing with it is the screen shuts off after 30 seconds of no user input. I stealth with it all the time, you just have to be really carefull when you check your levels. Battery life is great. I can do a 3 hour show and have 2 of the 4 battery life bars left. It's defintiely small (exactly the size and layout of the old original Nintendo game controllers). It has a "hold" feature which is nice when it's packed away somewhere. I bought mine outright when they first came out, so I don't know much about the soundpro's version. I've never had any trouble with mine.