I've had the TPCast for Vive for about 4 months now and regularly play for 4-8 hours on end without issue. The audio is fine, it's the mic that doesn't work but it can be fixed by using OpenTPCast (Discord) which is also more convenient than the regular software for starting up and hot swapping the battery. The colored lines are not visible in my HMD even with a slim face pad.

Yes the price is heavily marked up because there's no competition (I ordered mine from China for $270), but VR thrives on immersion and for room-scale play in active games like Echo Arena / Onward / Payday 2 the immersion is on a whole other level. I had to enable a marker overlay in the center of my 16x10 ft room because I'm moving around far more and without any pull from the wire or orientation cues I end up on the walls constantly. I've even lost interest in Pimax 8K because it will be a tethered experience for the next year. Tethered is fine for seated simulators, but has no place in room-scale play.