I use Capit's - same brand as some of the MotoGP riders use.
Plus they come with a 3 year warranty!
I also run Capit's. They have the best tech available in warmers today.
Do not run the warmers from that ebay site above, they are made by a particular company then rebranded by whichever on seller has stuck there brand on it on that particular day.
There is a known problem with the digital ones, so much so that when you do send them back they will send you non digital ones in return. I am pretty sure La corsa, Kaneg and those Moto GP ones and more are all the same.
Those three warmers are known for malfunctioning temp units and the elements are known for burning holes in tires if and when they do work they do not warm tires evenly.
Note how all the ones in the pics look the same...
If you buy cheap you get cheap!
The Chicken Hawk's, Woodcraft's or Sportsbike warmers are all good cheaper options than the Capits or Bandits and all of those will actualy work. If you want the best buy Capit, next in line to me would be the Bandits, again used in GP and WSBK Both have varied levels of warmers in terms of price and features and no you don't need digital ones. I run the Capit Maxima's, read up on them if you like http://www.capit.it/eng/accessoristica.aspx
Google every brand before you buy.