Okay look, the LG G5 was not a successful phone. There's little reason at this point to run out and buy one, but that doesn't mean there's no reason. LG just added the US unlocked model (RS988) to its bootloader unlocking tool. If you need a fast phone with an unlockable bootloader, there are worse choices.
Unlocking the bootloader on your device lets you flash unsigned software to it. That makes things like rooting and custom ROMs more feasible as you don't have to rely on sketchy hacks. LG's unlocking tool requires a supported device and ADB/fastboot working on your computer. You have to generate an ID code from the device and feed that into LG's tool. If it checks out, LG will email you an unlock file that can be pushed to the device over ADB.
LG still lists the RS988 at $650, but most retailers have it cheaper. The best deal right now appears to be B&H, which is only asking $400. They'll even throw in a free Cam Plus module (which I suspect you will never use).