I just looked up the specs for both the Galaxy SII and the HTC One VX and confirmed what you already know… An additional issue with the Galaxy SII is that using Samsung’s Android releases it doesn’t support BLE at all (according to the wikipedia page) even though the hardware is theoretically capable and can be made to work if you root it.
As for the HTC One VX, I’ll see if I can get the Android app building for earlier versions of Android soon, but right now I have to focus on fulfilling remaining orders and fleshing out some of the features still missing from the app. I’m very sorry to make you wait longer, I’ll try some backporting experiments soon. A lot changed between Android 4.1 and 4.3.
Let me know if there’s another way I can help in the meantime. Best,