The reset button mod is pretty much just for if you use an Everdrive, or want to play that one X-Men game.
Everdrive requires a soft reset to save SMS SRAM data to the SD Card, and Nomad has no reset button.
It's a simple mod, just solder the reset wire of the cart edge to a button that grounds it when pressed. If you use a simple AND gate IC, you can make it reset when you press Mode and Start.
I recommended the expensive one because fast load times, and it is what I have.
The point of the battery mod is to have an internal battery and not have to fiddle with the battery pack. you also get insane play time off of it, like more than 7 hours.
If you decide to go with AAs, the eneloop rechargeable are really the greatest batteries.