I just got my APM Ultraflat 30 mm a couple of weeks ago. Mainly I was motivated by the very positive comments about it on this thread!
I had a Kohki 30 mm Widescan II, which has a huge AFOV (a little bigger than a Nagler), but a lot of astigmatism in my f/6.3 triplet apochromat The astigmatism was visible but not too intrusive in an f/8 refractor. I held off buying a 31 mm Nagler mainly due to the weight and size. I hate having to lock everything down just to be able to change the eyepiece without losing the target!
In short, the Utraflat 30 mm is FANTASTIC! I've used it now over several clear nights. It really is pretty much aberration-free at the edge of field! No comparison to the Widescan. Pinpoint? Well, no, but no eyepiece is really literally pinpoint at the edge of a large FOV like that, even the Panoptics and Naglers. There is a tiny amount of field curvature (i.e., different focal points as a function of position from center), but really very tolerable. I can't compare with a 31 Nagler, but for what it's worth, compared to higher power Naglers and Panoptics I have, the edge of field in the ultraflat is just a tiny bit less sharp, but that may well have to do with the larger true field bringing out field curvature in my refractor.
I didn't measure the AFOV or TFOV directly, and that has been discussed at length earlier in this thread. But just sticking the the Ultraflat and another eyepiece up to both eyes like a binocular, it's clear that the AFOV is about halfway between a panoptic and nagler, maybe a bit less. So like 73˚-75˚? Definitely more than the 70˚ written on the barrel.
Anyways, I very enthusiastically recommende this eyepiece! It's really the only option for a wide field 30 mm that is so sharp to the edge AND that comes in a manageable size. At $260 or so, the price is surprisingly low.