I am also an avid lifeproof user (I've been using lifeproof cases since their original iphone 4 case) and like you I got tired of waiting and started looking at other options. I've tried both the redpepper and the obex and I've gotta say that I'm really liking the obex.
It is definitely big and bulky (although I think pretty much any waterproof case is). Comparing it to the specs on the lifeproof case, it's ever so slightly thicker (the nuud is .48" and the obex is .5", but I'm not sure how noticable that difference is). It is taller and wider than the nuud, though... I believe it's .1" larger in each direction. (Lifeproof has the dimensions for the 6+ nuud case on their website, so that's what I'm basing this on). The back of the case narrows significantly as you get close to the edges and the extra length and width really don't bother me too much. The redpepper case was about the same length and width as the lifeproof case, but it was significantly thicker... .6" compared to the obex .5 and the nuud .48 and the extra thickness of the redpepper case bothered me quite a bit. I much prefer the longer and wider, but thinner obex case. Because of the way the back of the case narrows it fits well in the hand and feels good too.
They seem to have made some pretty significant improvements from the iphone 5 obex case as well... the mute switch is now the lifeproof style and seems to work well (and is a bit easier to move than on the lifeproof cases too) and the rubber plugs for the ports on the bottom are reasonably easy to use. I think I prefer the plastic door that lifeproof uses for the charge port, but the rubber plug is better than the screw lifeproof uses for the headphone jack. The plug is quicker and easier to remove and it sits flush with the case... the lifeproof screw sticks out a bit and looks ugly and can also be uncomfortable depending on how you hold the phone.
The power and volume buttons work well and are flush with the side of the case, unlike the lifeproof cases where they stick out a bit. The only downside is that it can be a little difficult to find the right volume button by feel. They're textured, so you can tell that your finger is on a button, but there's not much space between them. I've definitely gotten more used to it over the past few days and it doesn't really bother me so much anymore.
The screen protector is what it is. I very much prefer the exposed screen of a nuud style case, but that's not available right now (there is the dog and bone case that should be out for the 6+ soon, but I suspect that it will be way too thick... even the dog and bone 6 case is more than .5" thick, so personally I'm not really considering that one). I get a little bit of a rainbow effect with the screen protector, but it's not bad and I don't notice it all the time. It's been a while since I've used a fre style lifeproof case, but I seem to recall that it was much more of a problem with the lifeproof case.
The only significant complaint that I have is the film that they use to cover the home button is not very flexible and it definitely makes the home button harder to press. It seems to be loosening up a bit as I've been using the case (and I think to some extent I'm getting used to it as well). Hopefully with a bit more time this won't be so much of an issue. Touch ID does work very well, though, and I rarely get any bad readings.
The other big plus is that the obex is available with a belt holster. I don't like carrying the phone around in my pocket... especially something as big as the 6+ and there aren't many waterproof options with a holster right now... even lifeproof seems to wait a few months after the case release before the holster comes out.
I may still get the lifeproof nuud case when it's available (and when a holster is available) just because I prefer having no screen protector, but I'm definitely happy with the obex while I wait.
