I've never used T5s so I can't make that direct comparison. I can say that the one 12" strip was pretty overpowered by my Power Compacts (2x96w) making the change pretty subtle. When just the LED is on, it was able to reach all the way down to the sand bed...but I don't own a PAR meter to know how effective.
Now, I only have 1 12" stunner on my 36" fixture. Now that they have 36" stunners I think that would be better.