Strengths: Practical, easy to install,uncluttered appearance, inexpensive and totally prevents chain drop for worry-free climbing.
Weaknesses: Have to know precise circumference of seat tube. It is seat-tube circumference specific and, of course, requires a round seat tube. I had an error in my calculations and got the wrong size which had to be returned for the next size.
Recommend it to all my biking friends -- road or mountain!