...and I say this based on my exhausting experience with various battery grips - with both OEM and 3rd party brands.
1. In those cases where the manufacturer (in this case Olympus) makes a grip for a particular camera (in this case the E620), I strongly suggest on getting that grip. Yes, it may cost a bit more, but the grips typically mesh perfectly with the camera - both operationally, in appearance, and ergonomically. The E620's grip is superb IMO, and everything matches the camera perfectly. 3rd party grips (in this case the Own User ones) are nice - but ergonomically and apearance-wise, they won't really complement the camera the way you would expect. Sure, they may be "cheaper," but if you're talkin' a perfect match, then that may not necessarily be the case. But if cost is the overriding factor, then go for it.
2. For camera models in which an OEM battery grip was never released by the original manufacturer, then getting a 3rd party brand (again, in this case Ownuser), will work out just fine. Because after all, if none was originally available, at least having another brand - regardless of appearance - should help quite a bit. In this case, I've found the Ownuser grips to be superb on the likes of the E-330, E-410/420, E-510/520, and E500. But with the other cams that have Olympus manufactured ones as an option, I'd strongly recommend getting theirs first.
Again, I've been so through so many battery grips from a variety of manufacturers, that it will make your head spin. But in the end, if you are truly limited by what you can spend, you can't go wrong with the Ownuser brand.
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