Well first thing about the connection, the site says it has a "Standard Connector: N-type female (50 ohm)". This should connect directly to your WAP's (router or whatever) connector.
Next as far as the power rating (150 watts). You will not need a "signal amplifier" for this simply because the unit itself is the signal amplifier. You may need a power amplifier though to supply the neccessary wattage to push the signal the required distance.
Lastly $41.00 is not a bad price but you could have made this for about $5.00. I have made a few before and they work GREAT!.
Here is an awesome site that covers homemade wifi boosters. Check out the link for the "Pringle Can Antenna". This is the style which I have made. The most difficult piece of equipment to get in this construction is the connector that interfaces with your WAP's connector. In most cases it is not a standard coaxial type connector. You can find these at Radio Shack sometimes but if not you will need to buy some wifi antennas and cut the ends off and solder the connector onto your antenna. The distance that these homemade boosters have been tested at are up to and including 6 miles! The downside is that this is a directional antenna and needs to be pointed directly at the expected recipient (which is the same as your store bought one).
Another one is the
Cantenna which is basically just a fancy pringles can booster that some company has decided to market. With either the homemade version or the cantenna no power amplifier is needed. If you decide to go with the homemade version follow the step-by-step directions on that site and pay extra attention to the lengths of the hollow tubing you cut to fit on your threaded rod. This is what determines the frequency that gets transmitted and received. The washers are used to filter undesired frequencies cutting down on noise and interference. If the washers are not spaced exactly as the site described the wrong frequency will be transmitted and received.
Also use a pringles/coffe can in pristine condition with no dents or holes in it whatsoever. This can is what will act as your waveguide (signal booster) and will be thrown off by even the smallest inperfection.