When you compare total lumens and lumens to watts used a MH conversion bulb is a good bit less efficient than a regular MH bulb plus on average they cost more, in some cases a good bit more.
But then if there are budgetary constraints they are a heck of a lot cheaper than buying a second light system to switch out for flowering and cheaper than buying a switchable ballast.
 
So are they great? Not really. Are they good? Sure they are. Are they a true value for someone who cannot just go out and purchase anything and everything that is tops? They sure are.
Another option that some like, and I think is good, is a dual-arc/dual-filament bulb that puts out both the MH and HPS light spectrum at the same time from the same bulb.
 
For a while I could find them in wattages from 400-watts to 1000-watts but now all I seem to see is 600-watt and 1000-watt dual arc/dual-filament bulbs.
 
I do not know if they just did not sell well so places stopped handling them or if there was some problem with the 400-watt ones so they stopped making them, at least until the problem can be solved, or what.
 
You can still find bulbs for a 400-watt ballast that have an enhanced amount of blue spectrum light rays but I have not seen the actual dual-arc/dual-filament bulbs for a while.