I have not used the Mol d'Art melters, but I use a very similar product from Martellato that I purchased from Chef Rubber. In short, I love them! They are the best fit for me and are practically worry-free.
To use them, I load in my chocolate (bars, chunks, or pistolles), set the temperature for 50C and leave them alone for a few hours (usually overnight or while I am at my "real" job). When I'm ready to begin production, I adjust the temperature to 30C and add 30-50% by weight of pistolles to seed the melted chocolate. Stir with a spatula and, as needed, a heavy duty immersion blender to blend in the last stubborn bits.
Some of the points I like... There are no moving parts or motors to break. I can leave them on overnight or for days at a time without worry. They're silent. They're easy to clean. I can come home to 3+ Kilos of melted chocolate that is ready to work within 20 min. They work wonderfully with pistolles, where some motorized machines don't.
One of the best parts is that I've been able to maintain nearly flawless temper for an entire working day with minimal attention. By this, I mean stirring frequently, checking temper and temperature regularly, then adjusting the temperature slightly as needed. For me, the Martellato warmers are a pleasure to work with and they give me wonderful results!
All that said, if you are not comfortable hand-tempering and are not willing to invest a little time perfecting your eye and skills, I would not recommend warmers for tempering. They are a kitchen assistant, but not an automated sous chef. I would not have purchased one when I first graduated from the program because I wasn't confident in my skills, but now I wouldn't be without one. Unfortunately, there is very little information about the machines and their pros/cons.
Let me know if you have more questions!