I have no experience with this particular model either... but I considered it for the same reason (less stuff in my tank). In the end I went with the 'normal' Pro and added in-line Hydor heaters which was both cheaper and IMO a better solution while still taking the heater out of the tank.
same here, i have one for my 120 gallon and very, very happy with it. I'm anal about the "look" of my tank and despise equipment taking room inside the tank, therefore i consider it a boon to be able to "hide" as much equipment as possible.
It keeps my tank at an easy 79 degrees, my caveat to the OP is that it may not be strong enough to boost temps for Discuss, but anything else will be satisfied imho.
Man those things are $400+ bucks!
Benefits to a Hydor inline heater: it is meant to be out of sight, you can have 2 so that if one goes out you have a backup, it's waaaaay cheaper to buy AND replace, ad possibly more powerful?
So depending on your budget, I think there are way more inexpensive options with the same "unseen' effect. I'm using a $135 eheim 2217 with a $39 inline hydor heater. Grand total: $174; less than half a Eheim thermal unit. Plus if it breaks....
I have eheim pro II thermo heater and the heater malfunctioned and cooked the tank. Luckily I caught it in time to save the majority of the fish. If you search on the forum, there are actually a few incidences of this happening. I purchased mine new off of ebay but the rep from eheim would not replace the necessary part due to this. It was going to cost me $150 so I just installed a eth inline heater. This is my one gripe about eheim, they acknowledged that this was an issue but wouldn't fix it on a warranty technicality.