I currently have a Nikor 4x5 tank/reel as well as the HP CombiPlan-T tank, as well as a Jobo 2561 tank with 2 reels. Of them my favorite is the Nikor tank/reel, followed by the Jobo if I use my unicolor base for constant agitation, I'll go with the Jobo tank/reels. For intermittent agitation I use the Nikor.
The Combi-tank has one main advantage over the Nikor, it's still available new, while the Nikors are only available used, and used products can vary widely in condition. My first Nikor tank made me wonder why lots of folks say how wonderful they are, as it was hard to load, and hard to unload, but when I got my second one that was in much nicer shape I found out why they're so nice!
-Mike