We stayed in Theresa's appartment with four friends and it was great! The location is very good - safe neighbourhood and just a two-minute walk to the underground which takes you everywhere in Prague.
The appartment itself is roomy and has got plenty of space, even for four girls and their clothes/make-up/etc. :)
Theresa is a nice host who responded to questions quickly.
On the whole I would fully recommend this appartment!