It's very easy to run the browser using the Ewin (start the Ewin GBA Loader, press L+R, press A to confirm, then run the browser as always from the R4 menu), but it doesn't work so well with patches (requires a hard reset if you use patches).
The EZV3-in-1 works well with either patches or the loader software. The problem with the 3-in-1 is that it's rather slow (and REALLY slow for big games, as you have to load them into NOR first) and it sticks out of the slot (only about a millimeter, but that bugs me personally).
I'll just list the pros and cons of each.
EZV3-in-1:
+ Very good software support, thanks to people like Rudolph and cory1492.
+ Supports the patched browser perfectly.
+ Near 100% compatibility.
+ Very good save support (with patched roms).
+ Includes rumble (albeit somewhat annoying rumble).
+ Functions as a RAM expansion for homebrew (up to 16MB)
+ Inclusion of NOR allows dumping of NDS games (it's EXTREMELY slow and complicated though - if you want to dump games, you're better off getting another slot-2 card, like the SuperCard)
- A little bit slow in loading small games, and has very long load times for games over 16MB.
- Sticks out a tiny bit.
- No realtime clock (but you can patch these roms to use them, minus realtime clock events).
Ewin Expansion Pak:
+ Near 100% compatibility.
+ Loader uses clean roms.
+ Wonderful build quality - doesn't stick out at all.
+ Functions as a RAM expansion for homebrew (up to 32MB).
+ Quite fast at loading all games.
- Pretty bad software support at the moment - all that's available is the official loader, since Rudolph et al haven't done anything for this yet.
- Saving currently broken in the official loader for 4kbit saves.
- Using the official loader is currently the best option for running the browser. Most patches work, but require a hard reset.
- Incomplete DLDI support in the current loader (1.4.0), so soft reset only works with R4, AceKard+, and N-Card (using different loader versions).
- No rumble.
- No realtime clock (but you can patch these roms to use them, minus realtime clock events).
To sum things up, the Ewin is technically superior to the 3-in-1 (rumble aside), but the software support is currently a bit disappointing, due to the lack of a third-party loader and a dedicated browser patch.