I've used a digi dx on my WSM for about a year and never had any problems. It has a pit probe and a meat probe. The digi indicates both actual and target temps for both pit and meat. It also has a few other features, such as the ability to ramp the pit down so as to lessen the chances of overcooking when away from the pit, an alarm, and maybe another one or two I've never used.
About 3 months ago I got a Pitmaster IQ 110 for one of my Weber kettles that I use for low and slow when I need more capacity than my WSM 18 provides. It's a simpler unit and only includes a pit probe. Pitmaster has since come out with a slightly different unit that seems to allow more control over the fan (came out about a week or so after I received mine). You can set the target temp for the pit but you really don't get a reading of the actual temp on the PM. It uses a system over lights to let you know when your 10 degrees or 50 degrees off target or when there's a problem. Like my digi, the PM has worked well so far.
The digi has more features and is built a little better (metal rather than plastic). I also like the position the digi adapter fits my WSM better than the PM, although I haven't had any problems with PM.
If budget isn't a problem, I'd go with the digi. If budget is a problem and you don't need the digi's meat probe and other features, then I'd go with the PM (or maybe one of the other alternatives). There is a pretty big price difference. I really can't speak to durability since I haven't owned either for very long. Both have worked as advertised for me.