I have the Tanklimate medium sized, (12x6x5 I believe) and I used it only once for fish so decided I would use it for smaller frags and for a couple mushrooms I need to get back on rocks. The three things I will say about it are...
1) The magnets are surprisingly stronger than they are rated for. My LFS got me the wrong one, (wanted the larger one, but got the medium sized one) and it is rated for up to 1/2 inch glass, but it is fine on my 3/4 inch glass.
2) fish love it to hide out in, (or just explore) because the lid does not stay on tight enough and they can easily open it. I had a Dottyback get stuck in the bottom underneath the frag rack twice and a large Foxface, (about 6") that likes to chill in it.
3) The slots do not allow enough flow for any coral that needs the flow so I would only use it for low flow coral. For SPS, I would strongly recommend a standard frag rack to allow proper flow.
Hope that helps. ;Happy