You actually never mentioned what kind of shooting you're doing most. Just my opinion, but for what I'm doing (everything off a tripod) I'd suggest the iPhone holder neither ALPA or 3rd party, main reason being that it is light and small (you always have a phone with you anyway).
The ALPA optical finder is very nice if you shoot handheld with a TC, but once you get into awkward positions for framing, sometimes an optical viewfinder becomes very unpractical.
Using the iPhone, with its very wide viewing angle, I find it very easy to approximate the composition with the camera in various positions, be it very low or very high.
For what I shoot I don't need super accurate framing, nor close focus or even tilt, so LV is just a nice feature to have, I don't want to be dependent on it.
The only thing is to remember to charge your phone!