I fail to see how much more ergonomic the GBA is versus the GBASP, even modded with the backlight. Could someone enlighten me?
You've got to be kidding. Have you ever held both?
The screen isn't quite as bright and no internal rechargeable batteries.
The screen is shit to view unless in perfect lighting condition (or Wiggy backlights of course) and internal recharcable battery is not pro in my mind but con, on the road you can simply pop in to any store and buy new batteries.
But yes the ergonomics is way better.
@Wiggy. read my PM and please help. 
I meant the new backlit LCD isn't as bright as it is in the SP
Got your pm, and your other goodie showed up today

I like that it uses double As. I'm leery of non-replaceable charger batteries. I have a kind of expensive wireless headset that I'm a little worried about. It's fine now, but in the future... who knows
Yup, that's a completely valid concern. Right now there are aftermarket replacements, but who knows how long those will be on the market
