i used one for my 10 gallon and had no problems. I have needed more since then and have made them myself using folder binders and plastic mesh, or for fry i use non slip grip stuff that you can buy in a roll from walmart for $3
Topfins are fine but like Stevenjohn21 suggest it is much cheaper to make them. You can get the mesh stuff at a craft store and the binders you can get at any store that sells school supplies. The binders are about $3.00 and the mesh stuff is I think about 50 cents.
Id just be worried about what to use for the dividers.. im a bit paranoid about what i stick in my tanks, so i prefer to pay the 10 bucks for one. I paid 16 bucks for the other, and its a bit overboard..