I have been using thingamabobber strike indicators for quite some time now. I have to tell you that they are by far the best indicator I have ever used. However, they do require some modification in order to get the best performance out of them. Straight out of the package they work just fine, but they do tend to slip some on your leader. I use the 1/2" size 90% of the time since they are perfectly sized for the smaller nymphs and midges I frequently use. Below is how I modify them to reduce line slippage and they even seem to reduce line twist.
First I buy a package of small O-rings from Lowe's plumbing department. The smallest size that I can find is usually just about perfect.
I then cut them and slip them through the hole on the indicator.
Finally, I super glue the O-ring back together.
When fishing I loop my leader thru the O-ring instead of the standard loop on the bottom.