The Nikon- and Canon-branded battery grips are insanely expensive. What alternatives are out there, and where is the best place to buy them?
I highly recommend Zeikos battery grips. I have the Zeikos grip for my 5D Mark II, and I could not be happier. It matches my 5D2 perfectly, with no flex. With two batteries, it gives it enough heft to match my bigger lenses. It has vertical shooting controls (which I never use), and sits firmly attached to my 5D2 body.
I bought it from Amazon, paid $90.00, compared to the $250.00 that Canon's brand grip cost.
Regarding reliability, I've taken it with me now on several shooting trips: Greece, Holland, Germany, Spain, France, Sweden and Finland, and it's never had a single failure.
I've not handled the Canon 5D2 grip, but the Zeikos feels identical to my canon brand 40D grip.
I believe they also make Nikon grips, but I can't speak to them, as I am a Canon shooter.
They are definitely a chinese knock-off brand, but the quality is surprisingly good, and if you need a grip and are looking to save money; you can't beat it.
Now, just a word of caution: while I recommend 3rd party grips, I can't recommend 3rd party batteries. I've read enough horror stories to stick with Canon's over priced batteries.
I have used the Opteka brand which was outstanding value for money. For example for the Canon Digital Rebel series, check this out:
For the price (at the time of writing), and given the inclusion of two 1800mAh batteries, it's pretty hard to beat.
The thing to keep in mind is that all of these third party products are reverse engineered and probably haven't been tested in every conceivable scenario before being released to the public. The cheapest ones and the ones that first appear on the market after a new model is introduced are often the worst. Some of the more reputable third party brands tend to take a little longer to get their accessories for new camera models to market.
For third party grips I've found that the 'Pixel Enterprise Limited' Vertax grips tend to be the most reliable and trouble free. 'Zeikos' and 'Meike' have been pretty good. I've never had a 'Neewer' grip but other 'Neewer' products I've used tend to be hit or miss at times.
If you want absolute rock solid dependability in a battery grip you'd probably have to break down and buy the manufacturer's branded grip - if such a grip exists. But OEM grips don't exist for all cameras. For instance, Nikon does not offer grips for the D3x00 and D5x00 series.
For other cameras that do have available grips offered by the manufacturer, that's normally the best solution for 100% functionality and the highest level of reliability. Sure, they are outrageously priced. But the only other options are all too cheap because the competition for third party products is all about price and almost nothing else but price. It's a shame there are no third party grip makers that make high quality grips at a reasonable price the same way the best third party battery makers make batteries that sometimes outperform the OEM batteries for 1/2 to 1/4 the price.
I once had a cheap third party grip for a Canon 7D Mark II that would sometimes "blink" for an instant. It would only do it occasionally, but it always seemed to be when in the middle of shooting a burst of action frames. Of course the instant power-down/power-up meant I lost all of the images in the buffer!
I finally figured out that at certain shooting positions the grip was flexing just enough to lose contact with the camera at the connection point inside the top of the battery well. In effect, it was like a computer that was being unplugged without being properly shut down first (and without an UPS). Once I figured out what the problem was I could easily reproduce it by flexing the grip in the wrong way. In defense of the grip in question, this only started occurring after the camera with grip attached had taken a pretty nasty fall from vertical to the ground while attached to a monopod extended at about 60 inches.
I've had another third party grip that would act a little flaky at times. It caused a control on the camera's body to not function. Rebooting the camera solved the problem until the next time it decided to do it. I've also had issues with the 8-way joystick being easily damaged or falling off third party grips for the Canon EOS 7D Mark II, but this is a known issue that users of the first party Canon grip have also experienced. So in that case it seems the third party grips suffer from a poor design copied directly from the original Canon version.
I had a Big Mike's grip for my 6D before it got stolen. It worked other than a curious quirk where occasionally (every few months, maybe) some of the camera's functions would stop working until I rotated the dial on the grip.
The batteries that came with it only lasted a short time before they stopped communicating with the camera, which seems to be a common problem with many LP6/LP6N knock-offs.
When I bought replacement hardware, I went with a Canon grip.
I have used a Phottix grip on my Canon 7D for some years with pretty good results.
I think I've had the odd time where the grip buttons wouldn't move the focus points, but powering the grip off and on again fixed it up.
tl;dr I'd happily buy another Phottix grip rather than pay the full price for the Canon grip.