Stop stressing your frame by over-tightening your 15mm bolts just to keep your chain tensioned. The Surly Tuggnut Tensioner allows for easy chain tensioning with the twist of a screw, and you won't need two feet of leverage to remove your axle bolts anymore.
Strengths: Works extremely well and consistently. Can be adjusted by thumb thus eliminating a tool from the kit I take with me. Really does open a bier. It's design doesn't insert into the drop out per say. So you don't have some insert or metal extrusion that you have to hack saw off to fit into the drop out.
Weaknesses: Price 35 Euro with shipping for a few pieces of metal.
This chain tug works the best out of all that I tried. It pulls straight, gives me confidence, opens bier, helps with setting chain tension correctly, but seriously 35 Euro! well in the end you do get what you pay for. It's just ridiculous that someone in china is not already copying this and selling for less. Surly you did a great job of making a great chain tug.