I have recently bought VIE 5217 Feedback Decoder as an alternative to Maerklin's s88 feedback decoder in order to connect it to my 6051 Interface for track occupancy feedback on my layout.
I am almost ready to install it but just realized than Viessmann offers also 5233 which is a feedback decoder with track occupancy detector???
I checked VIE's catalogue trying to find more info about the differencies but it doesn't help.
Does anybody know what are the differencies? Have I did wrong to buy 5217?

The 5217 can be connected to reed switches, contact track, circuit track, push button, etc. Exact duplication of s88.

The 5233 counts as 1/2 of an s88 (or 5217). Track power runs through the 5233 for 8 blocks. When a Lok or lighted car (something with a slider) moves into the block and draws power, you get the same s88 signal as a circuit track (or reed switch,...).

Best thing, you can run overhead power through the 5233, and can then detect E-Loks without sliders.

No direction information; you get the same signal for either direction.

Hope this helps!

BTW, Litfinski makes these too. (I plan to use 4)http://www.ldt-infocenter.com/english/home_frame_e.htm
Even if you do not use his items, his diagrams are the best!