My basic recommendation for a fuge is 10%-20% of your display volume. For your tank a 10g-20g fuge will be just fine.
The link you provided I would avoid. There are HOB
fuges that are dedicated fuges. For your system you are going to need a lot more in the way of a skimmer then that can provide.
I would look at something like this HOB Refugium
. This is still only 6g but it is closer to what would work better for you IMO
I would also check on Ebay as you may find a good deal there. Check in your local area for a reef club you may find a used one for 1/4 the price.