"Mh doesn't give off the proper spectrum of light that the plant needs in flower."

That's a huge misconception. In fact, MH puts out MORE red and blue which are the critical components for flowering. HPS puts out more green. HPS was designed as human lighting, not plant lighting. This is why you're seeing HPS bulbs with 'EXTRA BLUE' - they're lacking what the MH isn't.

"When flowering the plants need more of a red spectrum"

Proven totally false in my blue-dominant flowering experiment. Please see the link in my sig. As an added note, it appears that any higher of a photon flux density per wavelength might be a waste. I still have to sort that out but my blue-dominant results still stand out. I've also successfully flowered multiple basil and cacti types under blue-dominant lights (most recent being Euphorbia obesa.)

"That is the way all the pro growers do it "

Funny you mention that, as every commercial and truly professional food production place I've ever come across (that's to say, in my travels around the world, Holland, Morocco, UK, Australia,) will tell you HPS is a piece of garbage. Those are pro growers. They've got the degrees, they've got the testing equipment, they have the decades of experience keeping people fed.

People choose HPS because it's cheaper than a CMH or MH bulb.

MH is the actual professional standard. And that's going to be that way for quite some time, until other lighting solutions finally start pushing the PPFD of an HID.

Hey Dutch - I just finished making my CMH killer. Maybe I can get you to test it out sometime.