There are several options for upgrading one's lighting. You need to consider all factors to ascertain the true cost of your upgrade. For example - are you using a glass top? If so, will it accommodate a 2d strip? Or a 2 bulb strip?
When I was upgrading the lighting on my 30gal, I considered every option I could think up, including a 2d strip, a 2-bulb std flourescent, cf fixtures, and retrofits (AH and others). I went with the AH 55w. It was the cheapest way to get that amount of light, and since it fit into my existing strip fixture, it worked with all other aspects of my setup. Also, it was a single purchase/shipment, instead of buying a fixture, plus a glass top, plus whatever else.
As far as the lighting amount - 55w on my 30 is okay, but it does impose limitations. I do not think it would be at all excessive on a 20H - even for a beginner. YMMV. I'm undecided on whether I will go with 4x55 or 4x65 on my new 55gal.