On an N3DS, the DSTwo+ is probably better, because I hear all the GW 3.5 Launcher really adds is support for 10.3.0-28 for their rom selector and cheat support.
The 3.4.1 Launcher and the 1.03 GW Emulation plugin for DSTwo+ is said to not contain the brick code yet, so on a N3DS, you'd be able to stay on 3.4.1 and because you are limited to 9.5 emunand anyway, rom selection should work fine, just no
cheats, but no brick code in the launcher (supposedly), so it -should- be safe to use.
And then the card also supports DS roms and decent GBA/SNES emulators, but on a N3DS you can already get fullspeed GBA and SNES emulation with
3DS homebrew especially when on <9.2 with kernel access.
I guess it's mainly the convenience of both 3DS and DS on one cart without having to switch.