Cool, I definitely didn't want to offend you. I actually tried to delete the post, but I was on a tablet and the tablet form of this site does not allow you that option. Later, I tried on my phone, still no luck. By the time I got to the home computer, I just figure it was too late.
It is an Aquatop. I have no personal experience with them at all. I don't know if they are good/bad/acceptable/not. After the previous link to them, I did some web surfing. If they are what they say they are, it impressed me. If they made one slightly smaller, I would get one for my 20L.
I found this:
Aquatop CF Series Canister Filters with Built-in UV Sterilizeer - YouTube
which shows assembly, set up, and maintenance. About the only thing I've been able to find negative about them is that they don't come with enough bio-media. But, if that is the only gripe, that is taken care of pretty easily for not much money.
The CF 500 might be a bit much for your tank. I try to shoot for somewhere between 6 to 8 times the turnover rate for a tank. For a 56 gallon, that would be between 336gph to 448gph.
The CF500 is 525gph, which would turn the tank over 9.4 times and may cause current issues (depending on the fish you use). However, it does come with a spray bar, which would limit direct current flow but still have a high turnover rate.
The CF400 is rated at 370gph, which seems about right. You can find them on Amazon with free shipping, but you'll pay tax. You can look at Buy.com and they have both free shipping and no tax.
Buy.com - AQUATOP CF-400UV Canister Filter with UV Sterilizer - 370 gph
I would do your own research and maybe a search for reviews so you can feel comfortable with your purchase. Again, I have NO personal experience with these at all. I can say I love my Fluval and wouldn't have ever tried a canister except I got it for free with the purchase of the tank off CraigsList. Now that I've had a canister, I'll never go back. Just my personal experience though... that and five pennies get you a nickel.