Tell me more about this little guy will you? I've been looking for a small emulation/arcade machine to run stuff up to PS3/Wii games, and it looks like I can use this with a GPU slot. Low profile right?
How powerful is this little guy comparable to say, an intel i3 third-gen (ivy-bridge) or something?
Or is it better to get like an old HP 8300 SFF and throw in a low-profile GPU?
Not for the PS3/Wii, you won't. The HP 8300 probably won't cut the mustard either.
RPCS3 needs at least a Zen2 (Ryzen 4000 series) or a Skylake connected to something like an AMD Polaris or an nVidia Maxwell. That'll require at least an HP t740.
As for the Wii...eeeeh, no. For something playable on a game like Super Mario Galaxy you would need at least a Kaby Lake or a Ryzen, and if you want BOTW? That's probably Ryzen 2 or an Ice/Tiger lake. If you are dealing with Gamecube with multiple on-the-fly shader recompilation like Rogue Squadron 2, that would be Ryzen at the very least as well. Even for playable PSP games you'll need at least a Haswell Mobile.
For something like the GX-424CC (embedded version of the AMD A8-6410 Beema laptop APU)? It probably runs like a Sandy bridge i5-2520M or an Ivy Bridge i5-3317U. Not really enough for anything heavier than, say, N64/Dreamcast emulation. That GPU onboard? It's GCN2 based. Probably okay for PS2, PSP or N64 games, but anything heavier for emulation and it'll not work well.