I bought the VV Mobile from European Marine and installed it on my 115 Pro XS. Very simple install and worked perfectly on my iPhone. I now know how accurate my analog tach is...its about 150-200rpms fast at WOT. Vessel View showed my Tracker PT 190TX doing 50mph @ 6200rpms. Analog showed me turning about 6400rpm with analog speedo registering 55mph.
In addition to accurate tach Vessel View provides gps speed, engine temperature (136degs at WOT), fuel consumption, engine hours(currently only 16 hours on engine), and voltage. If I ever get an engine fault code Vessel View should decipher the code for me into english and indicate the severity of the issue(take to dealer immediately or it can wait for a while).
The Mercury Spitfire X7 19" is very smooth throughout the power band. At the highest trim I can get I can feel the prop starting to get a little erratic. Almost like one blade breaking loose. Air temp this morning was high 70s and engine only has 16 hours on it so I expect things to get a little better as temperatures cool this Fall and the engine gets thoroughly broken in.