Well generally Mars will veg ok but not flower very good, probably partly due to the claims they make about the wattage and comparable to x hps. They are less efficient than HPS so will be hotter although may not seem to be because they have fans dissipating the heat faster into the grow room.
There are lot of poor quality LEDs on the market which will be much the same.
These guys with there COBs LEDs are claiming around 1.4gpw and running lights which can be almost twice as efficient as HPS so you really can use less watts to grow the same or more weed. I use the word "claiming" only because my COB light grow is way off the flowering stage, I do believe all the folks on here and have seen some evidence of the higher gpw and evidence of what they are capable of.
As said above check out Growmau5 on youtube, not only does he have a 7 part series on everything you would need to build one (sounds complicated but its not) He also shows his comparison of HPS side by side with COB LEDs. YouTube is full of folks making bullshit claims by people paid or gifted shit to market products, he is not one of those guys.
If I remember rightly he was pulling around 0.85gpw from his HPS set up and has pulled off 1.4+ gpw from the same wattage COB LED light. If you check out his early vids you should find the comparison. He also shows all his dry weights and shows close up bud shots to prove they are not airy but dense nugs.
Anyway, as far as LEDs go that what folks are doing these days. Problem is the old tech blurple light companies have flooded the market with misinformation and cheap shit products which casts doubt on the whole LED world. The fact is there's cheap LED and quality LEDs and they are worlds apart.