It is kind of like a removable partial verses a fixed permanent bridge with teeth. Removable is moving or loose all the time and chamber adapters go in and out or at best up and down. In teeth they are hard to chew with but better than nothing. Fixed bridges and fixed chamber sleeves both stay in place when they work well you can chew or shoot just like normal. Cost is often the deciding issue. If you can afford chamber sleeves that stay in for ever they will be the most useful.
As to claims that a 28/20 will out perform a 28/28 you may be able to show a on paper difference. But can you use a 2% improvement and really improve your shooting ability? Not likely. These chamber sleeve just give you options and help restore badly pitted guns.
Also if you use fiber wads in a sleeved gun you will get a poor gas seal and blow by of gas with decrease performance. Plastic wads may seal enough but felt wads will not. Some shooting venues are requiring fiber wads instead of plastic wads.
