I do believe that they could have been flowered under the T5, although it would need good side lighting, but I'm extremely happy with the HPS , I still may do some side lighting, since everything is so close together in there, but HPS is definately the way to go.
And this is still a T5 grow, I have 2 cabs, 1 cab has the T5 and is vegging 5 clones, my other cab has the HPS and is flowering the 5 ladies.
But Id say you can easily get your money back from buying an HPS 10 fold. If you only have 1 growspace, I would just spring for a convertible ballast and get a MH and HPS bulb and switch them out when you go to flower, HID is where it's at.