When I was looking around for an Alfine bike, proper chain tensioning was a must have. The tensioner should be a last resort for conversions, and fitting one to a factory model is poor design.
The 2008 Merida S-Presso had vertical dropouts and tensioner but the 2009 version is much improved with horizontal dropouts, no tensioner and excellent brake location. Alfine is such a nice system it deserves a properly designed frame.