There are two types of Chinese Knock-Off right angle finders. One has both 1x and 2x (or 2.5x) viewing and the other is restricted to 1x only. I would opt for the viewfinder with both the 1x and 2x selections if I were shopping for one now. The difference in cost seems to be minimal if there is any difference at all.
That said, I have the Seagull that only has 1x and it suits me just fine. I love the right angle finder because I have modified a SLIK Pro 330DX tripod with a short center column and an F1 Adorama Flashpoint Ball head. The combination is really nice and it is very light (2 pounds and 11 ounces) but, it is pretty short, elevating only to 4 feet. However, the right angle finder helps me and since I cut my photographic teeth on twin lens reflex cameras, looking down to frame and focus comes as second nature to me.
Another use which few people try, is using the right angle finder when photographing standing people using wide angle lenses. The natural distortion of a WA lens will often cause a person's upper torso to look a LOT BIGGER than the lower torso because you are shooting down from eye level. The right angle finder will lower your point of view and reduce the distortion somewhat.
I cannot speak for the Canon, but the Seagull seems to work fine. The Canon model would need to be a lot better for me to choose it since it is drastically more expensive. BTW, I have seen right angle finders for as low as $30 on eBay. If memory serves, I paid less than that for mine which I also bought on eBay.