The MIMO depends on special Antenna arrangements; it might not work well or not work at all with standard devices.
It is very hard to significantly boost long range of 2.4 GHz with Omni directional Antenna.
Expression like 600% are marketing Ploys since it imply like if you can reach 100? it might easily extend to 600?.
Instead of wasting your money on lame MIMO and boosters, buy two 802.11g Wireless Routers make sure that one of them can be fitted with external Antenna.
Place the Second Router in window facing your Friend place put a Directional Antenna on it, connect it to your main Router via CAT45e and configure it as an Access Point (
Using a Wireless Cable/DSL Router as a Switch with an Access Point ).
If your Friend gets the signal you are set other wise you need a similar arrangement on the other side using Group Bridge instead of the second Wireless Router (like the WET54) on the other side.
:sun: