Seriously, GBA Games, Rumble (I find it helps with EBA and Ouendan, because the rhythm for "when you get a hit" doesnt always match the music, but it always matches the rumble), and RAM (The Opera Browser isn't amazing, but it's alright - and I use DS Linux a lot; oh, and Quake
Do not buy a new one, try to find a older version. EZ-flash AS stop production of it "3 in 1 expansion pack" in mid december 2008 to replace it with the "3 in 1 expansion pack plus".
If you buy a new one It is not write on the box that is a plus version and the only way see what you receive is to use gbaexploader 0.58b and it says at the top of the screen (3in1pls).Expansion ram and rumble it not detected anymore with the "3 in 1 expansion pack plus". Event Dsbowser and Dslinux do not detect the extra ram. Only the utility gbaexploader 0.58b will play Gameboy roms.
Do not buy this if you do not have the EZ-flash V cart to go with. It not working anymore with other cart like Cyclo evolution, Acecart, etc...
its only a matter of time until rudolph finds the right code to use the expansion ram. DO NOT, and i have to repeat -- DO NOT -- buy a 3-in-1 for rumble. it drains the 3v battery you need for sram saving and it basically sucks. you would be better off buying metroid pinball with the retail rumble pack if thats all you want. tell you dad that a 3-in-1 will allow you to play a library of over 2700 gba roms and 400 known gba homebrew games/apps. not to mention you can flash any .ds.gba game/app (well anything under 32megs) over to the nor and launch it via passme using your slot1. eventually when cory or rudolph are able to get the right set of code to boot the ram the opera browser, linux, quakeII, etc, can all be played with and enjoyed.
if your dad still isn't sold tell him you will take out the trash for 2 months. the thing only costs 19 bucks as it is. you could always collect pop cans and return them for the 5 cents.
The 3v battery is here to maintain data in SRAM memory not to make the rumble works. The power for the rumble's motor is taken from GBA bus as far as i know.
If it's not the case then your ez 3in1 is defective.