HTGsupply.com/MH-HPS Ballast Question

This site on eBay is pretty sweet and I want to buy a new light. The have seperate MH and HPS ballasts, and one that will light both. I have the one that lights both, it come with two bulbs and a free (?) timer.

I asked them if a staright HPS or MH only balllast they sell would light either/or bulbs because the ballasts are less expensive. They do not come with two bulbs and the free timer.

They said no, I needed the "combo" which was more expensive. But after reading the description of several lights they have, they seem to be the same ballast.

Below are links to eBay and the three examples I was looking at.

I really don't need the extra bulb or timer. But are the ballast REALLY that special that I need the combo?

MH: High Tech Garden Supply

HPS: High Tech Garden Supply

Combo: High Tech Garden Supply

Thanks for your imput!!!

see if this helps you understand ...

How to wire your own Marijuana Grow lights &Save Money & Wiring 2 Rooms With 1 Ballast,

You only need the combo if you are going to use the mh to veg and the hps to flower, i have a combo because it only cost a bit more. the electrical demands are different even tho the lumens may be the same for each light.
dont bother with the switchable if you using floros to veg, and hps to flower, a combo that i think works fine.
i got the switchable as a free upgrade for buying the setup as a complete unit, (light, ballast, and hood) so i didn't complain, but dont think i'll ever by a mh light unless i started growing more seriously.

those do seem like the best deals i have seen around . i think i'll go for a 400w hps kit

do it, check these out. my first grow. seeds from visc