The Good: Two way shifting (push/pull), custom side to side positioning, crisp index shift, easy to use cable port
The Bad: All plastic casing, no shift level adjustment, no I-Spec compatibility
The SLX shifters came as OE on my bike, but I have been really impressed with what Shimano has done with them. They are a very good choice for a mid-level shifter. My shifters are a 2x9 set up with no gear display. Shifters have a nice crisp index shift, that isn't too hard or too soft. Once you are in a gear you know, and it's definitely not a shifter that will allow you to be in between two gears. Do wish they came with a lever reach adjustment, but this is a feature that you'll find on more expensive shifters.
These shifters do have one really nice custom adjustment feature. The SLX shifter pod and handle bar bracket are two separate pieces. By doing this Shimano also made it so the shifter has multiple side to side positions allowing you to "slide" the shifter closer or further out. Wish that these shifters would have been included in Shimanos new I-Spec, but the SLX SL-M670 I is.
One last thing is the ease of service. The shifters, like many, have a small hole in-between the shift levers for changing out the shifter cable. I recently did this and was done in no time at all. Just make sure to take your time putting the cap back in so you don't strip it out, it is only plastic.
Overall I think this are a great mid level shifter and in the year I have had have done me well. These are shifters that once replaced will definitely be kept as a back up or make their way onto another build.