Are all MH RX7 lights the same?

I've got a chance to buy a box of 10 Metal Halide, 150W light bulbs. On the face of it, they are the same as the ones in my Aqua Medic canopy. The fitting is the same - RX7. The big difference is the price. At my LFS in the UK, one bulb costs £50. I can buy a box of 10 of these for £70 so if they are the same, it's a no-brainer..
From people's experience, will they be the same? They're definitely Metal Halide, 150W and look the same - box says they replicate daylight, producing 4200 degrees K. A bargain or a gamble?

 

Remember good ole' Roy G. Biv??

R ed
O range
Y ellow
G reen
B lue
I ndigo
V iolet

4200 won't even get you to the yellow range. Those bulbs are in the red/orange spectrum and would be good for growing plants. In an aquatic environment, that would be microalgaes and phytoplankton, cyanobacteria, turf algaes, and macroalges.

People started this hobby with 6500k's but hated them because it made the tank look yellow. That's when people moved up to 10,000 k for a whiter look to the water. Now, there are 12,000 k all the way up to 24,000 k bulbs for people want bluer tanks or people with deepwater acros.

 

4200k might be good for growing plants. Definitely not good for lighting reef tanks.

 

That clears that one up then... Thanks...