It's the fact that I know proper support will never be available. I have had @ 1 1/2 years experience with EZ support, and in comparison to SC it sucks big time.
For example, the EZ team have been working on DS roms for around 9-12 months and still have not manged to get 'pokemon dash' (amongst others) working on any of their carts. OK 'pokemon dash' is crap but that's not the point, it's an example of how they are not as good as the SC or M3 teams. I'm convinced that the EZ team will never have the skill to get that rom running.
Lots of the DS games that run on the EZ4, glitch and stutter, where they run super smooth on the SC.
But mostly ... it's the experience of 1 year of waiting for the EZ team to sort out their software with an unbroken sense of dissapointment on evrything they release. This is not a feeling I have with the SC team, they actually fix things, and from what I hear the situation is the same with the m3, they actually fix stuff too.
Why I bought an EZ4 I don't know, but I do know it was a mistake as the last DS game fix was almost a month ago. And now the reports of them being too busy with other projects to advance EZIV software further (it hasn't even got GBA rom compression!! )... same story as always. (always excuses for such along time now)
edit.. there is a whole host of bugs I could mention with the EZ4, most of which i'm sure will never be fixed.
just another quick example (there are many, this is just small example where even more bugs exist right along side )...
... GBA games do not run properly from the DS menu !! (I'm also noticing more and more GBA games don't run/save every day in either menu) /... to run GBA games without 'jerk' you have to boot in GBA mode (hold select.. flashme). In GBA mode the Save file backup takes up to 30 secs to a minute before the menu shows up. will this ever get fixed ? I would put money on it that it never does.