ok lets look at tubes for a minute the avarage 4' tube puts out 1250-1600 lumens that is distributed through out the 4' lenth of the bulb and consume 40 w an hour Now lets look at CFL's they put out (13 watters) 650 lumens while using only 13 watts an hour. The light is directed from a small source 1 1/2 inches or so. Now look at the energy that if you combine two 13w cfls for a 26 watt draw with the same amount of lumens (close anyway) The energy saving would is worth the cost of theese bulbs.
How many 4' tubes could you fit into your space. You can use alot more cfl's in the four feet of space that the tube would of taken and have a shit load more light.
They do work for flowering however they are a very weak lighting source compaired to HID.
Floro's will and do produce buds however the buds will be small and looser than those grown with a Sodium Vapor or Metal Halide. If you insist on using floros you can grow some real nice green with compact floro's (CFL) or T5's. T12 floro's just dont cut it for great buds. You can use T5 tubes and get great results, but if you are thinking about costs for growing lighting can be an issue and the most for your money you can get is out of a metal halide system. It would take 42 40 watt t12 floro's to produce the same amount of light 1 400 Metal Halide bulb produces. T5's you would need ten 54 Watt bulbs. 5 compact floro's 125 watts would produce the same as one metal halide as well. So if you really want good buds and save money doing it invest in good lighting.
Here is a good web page to compare lighting:
ACF Indoor Plant Grow Light Information Guide