Hi,
I cannot even tell from the link how the filter works or any of the specs for it???
I can say that goldfish are heavy eaters and need a good filter...
You may want to use a canister filter or two instead. A Rena II or Ehem 2217 series maybe? A magnum 350?
I would NOT base my decision solely on ease of maintenance no matter what the LFS told you. It should be a consideration point but that is all. If easy to clean but does not handle the load, what good is it?
What do you EXPECT of the filter and will the filter do what you want of it? What if things change? Do you have to replace or upgrade or can the filter handle the new requirement? Those are the real questions. Will you use the outlet to run a c02 reactor or pass through a UV or inline heater? A canister may give you more options down the road if your circumstances change...
Hope this helps.