I know I keep saying this (about more videos) but I'm working on it! As time permits....
The GDS does do alternate triggering but it looks like the wfm/s rate drops fairly dramatically. Not that that's really an issue since, well, you're using alternate triggering so you should expect it to drop.
Overall I've been enjoying it - it's easy to use, the response from Instek has been fantastic to issues I've brought up, they've been releasing firmware updates about every 3-4 weeks right now which you can take two ways: a) they have a lot of bugs or b) they are resolving them as quickly as they can. I prefer "b" but having dropped $1700 on this thing I may be a bit biased.
If you can I'd jump to the 2204 instead as you can't upgrade that later (4 channels vs 2). Not critical but in for a penny, in for a pound kind of thing.
-Greg