Is a reflector really necessary?

currently im about to start a new grow and Im in the process of ordering all the equipment and I was wondering if it's really worth it to buy a reflector. My grow chamber has mylar throughout it so it's reflective, so I was wondering if it really is wort it buying a reflector. I was going to order a reflector something along this line because it was cheap:
http://www.progressive-growth.com/proddetail.php?prod=38017

Can someone tell me if getting a reflector is really worth it and which one should I be getting? Any links would be highly appreciated

ps. Right now i want to use 600w hps for flowering and 400w MH for vegging

definitely brother....take it a 100% invest in one and ur ged rewarded with say atleat 15-20% more on ur crop atleast id say..

not necessary, but why deprive your plant of light? you can grow a plant under a single cfl, but growing bud is all about optimizing everything you can. reflectors, nutes etc. if you dont have a reflector then make one. or arrange you lights so that lights are getting as many parts of the plant as possible, side lighting is key. All light shouldnt just come from above.

it is essential.
the mylar is used to reflect the light, but by the time the light gets back from the ceiling to the plants it already pass through quite a distance.
a 600W is effective for 1.2m while the closest 50cm are the more effective part and getting more intense as you get closer.

a reflector makes the lights that would travel a long way to the ceiling and back travel only an extra few inches.