I'm not sure about the not needing a light thing, as apparently diamonds need UV? I dont know, They aren't really my cup of tea and I dont keep them, plus its too hot up here for them to live comfortably, so cant help you on that part...
But I have experience with heatmats, heatcords, and lightbulbs...
Lightbulbs: Blow frequently and easily, preference is to put a cage round the bulb so as to not have your snake burn itself by wrapping round it or whatever... I personally only use bulbs for my Dragons, as they need UV etc... Otherwise I would use another heating option...as it works out too expensive replacing the damn bulbs so often... Also takes up a fair amount of powerpoints etc if you have a lot of snakes etc. Also times that by your bulb wattage, and adds significantly to your power bill...
Heatmats: Not as high of a risk burning your python, although some have had snakes get burns etc from them... Wont Blow like lightbulbs...and hence dont have to be replaced as often and hence cheaper in that respect... Although does take up powerpoints and contribute to your power bill like lights. I just use them for my geckos as it is easier to heat them that way I find...
Heatcords (my personal favourite): Probably the least risk of inflicting burns to your python... Flexible, can move to suit, etc etc etc... Can use one long cord to heat multiple tanks, hence less powerpoints used, and hence less of a contribution to your power bill i.e. only 1 80watt cord as compared to 10 or whatever 80watt bulbs or mats or whatever...Dont blow like lightbulbs, and not as much of a risk of hotspots, can space the cord according to how high or low you want the temp and eliminate potential hotspots this way. I use 2 80watt (9m) cords to heat all my 10 snakes, and they get 2-3 runs of it under their tanks too. They cover a fairly significant distance/area! And you arent restricted in any way like heatmats in respect to that... This is the most efficient, safe and cheapest method to use for pythons IMHO, others may disagree with that statement, but I have found no probs or dramas with it, except for it can be annoying how they dont stay in the place you want, but I have found those closeable clip thingos work a treat to hold them in place etc so no real dramas apart from that, which I rectified!
Thats all I can think of on the pro's and con's atm, others would be able to add to it though, as I know there are some points I have missed... But hopefully that helps you...And makes sense...