A few people have been scammed on the site, Only use paypal to pay for items for sale by other members. If they will not use paypal, its likely a scam NEVER SEND E-TRANSFERS OF ANY KIND.
I love my SJ4000. Someone on this forum pointed out that you can get a waterproof charging case for $20. It will cost you over $100 for a waterproof charging case for a GoPro!.
I plan to leave mine permanently mounted on the bike dash-cam mode using the waterproof charging case.
I have the SJ4000 as well. It's a good unit for the money. Battery life is not the best, but there are options around that.
If you consider the SJ4000 a clone of a GoPro, be aware that there are clones of the SJ4000. The SJ4000 clone is even cheaper yet, but I think they still work OK. There is a web site that describes the difference between the real SJ4000 from SJCAM,or the clone that is also called an SJ4000, but not made by SJCAM.
I've seen some videos posted that had 'overlays' showing combinations of speed, compass and I think even bike info like gear, revs etc and one that even seemed to use a Google-type map off to one side similar to a racetrack overlay. That seems pretty cool but how's it done? Anyone here on the forums have any actual experience with doing this? I've looked at a couple of search engine results for overlays, so I'm not looking for links but for actual experience. Thx.