for grid/form data entry they work fine, and do quite well, there are some gotcha's,
a lot of the examples are not the same, so one example that works, will or may not work with your setup or needs.
as a inline edit mode entry(edit mode as default)., (store front), the performance sucks. I had to switch to infergistics for that functionalty
controls are good, and have excellent functionality.
So, based on say management of data, and database items, good and workable.
ecommerce site with field for entry , (edit mode constant), find something else.
scale of 1-10 for ease of use, 3....
I will make some caveats, I have only used them a short time, I am a database programmer of 20 years ,and only have done 3-4 simple/moderate asp.net websites. and 2 years in C#....
I am big on performance , so having my fun.