I think that will be the case in all of these action cams with small lens/sensor setups. The EWAL lens (extreme wide angle), more than wide angle less then fish eye, causing that noticeable parabolic skewing. Not sure if we're talking about the same thing (horizontal lines?).
Might be less noticeable as you shift the focal point towards the main subject, but on the sides, vertical lines will begin to shift (post correction possible to some degree depending on how bad it is). Since most users are buying them to film themselves it makes sense with the EWAL but it'd be nice to have the option without it or a conversion adapter, which I do not see possible for a screw on on these.
Wide open shots will be more noticeable, closeups and extreme closeups will get the benefit. Since these are such a small package you could pack these in and use them when needed. I'm just looking for another 3D rig besides an all in one solution. All of the all in ones A. have fixed position lenses and I'd like the option of widening out the I.A. (EWAL will have an impact though) B. all in ones (besides the Pro 3D rigs like my 3DA1) all have a compressed combined bit rate which lowers quality. With 2 separate compression files should improve quality over most all in one Prosumer 3D cams.
I haven't settled on anything yet. Just looking at all the options. I checked out the Nabi:
and the price point really isn't bad. The viewing angle is slightly less than Nabi HD at 160 on the GoPro vs 175. Not sure on the Ricoh, I think around 150 deg. Yeah, the Nabi looks to be really compact design and smaller lens, so wider angle makes sense on it. But not good for overall PQ.
Here's what I could find on each:
GoPro 160 deg
Ricoh 150? deg,
Panasonic A100/500 160 deg,
Sony HDRAS100V/W here's another one -with 170 deg
Canon VIXIA mini X 150/160 AVCHD or MP4 respectively
Also, some of these have image stabilization which narrows the field of view, but in practice I'm not sure how that effects performance since I haven't used any of these yet.
Sony's action cam boasts some pretty good specs from what I've read. Carl Zeiss glass, Exmor sensor, XVAC codec with 50 mb recording. 24p native support. And the price is 299, not bad. Not much on looks though.
I'd say the biggest drawback on these action cams beside the EWAL is the lack of zoom with the fixed lenses. I see the Nabi has a 4x zoom. It'd be nice to change focal points and as far as I know, the Hero 4 is still fixed focal. They work for what they're designed for, I know I'm asking for it to do it all...
A lot of drawbacks to these, but size and weight could make it worth it.
One I was just looking at Canon VIXIA mini X:
This one has 150 deg AVCHD or 160 MP4, also it can do 24p natively. Plus Canon glass and LPCM audio instead of compressed on most others, but with a cheap mic, probably not much difference there. No zoom here either, fixed focal.
Still GoPro has the best all around features that I've seen.
Update: On the Sony POV, I'm reading great things about it, one big advantage is the image stabilization which the GoPro doesn't have. Maybe the Hero 4 will finally get it? With the stabilization on it narrows the angle down to about normal level so easy way to record without EWAL. And a correction on native 24p, it does over cranking 120 or 240 over 24p, not normal 24p frame rate. Records in 60i/60p only. One advantage on the new Hero 4 is 120 fps in 1080p, but at 200.00 more. The only one of these with native 24p support is the Canon mini Vixia.
Getting a little out of the action cams: CANON VIXIA HF R500 Black
Price is 299.00 and offers a 57x advanced zoom. 35 mbps mp4 recording, 24p native. Several IS modes. A little bigger though at 8.5 Ozs. 2 of these might make a nice bench rig. I've got a few months before I buy so no hurry for me.