I think It would be great  the AUTOCOMPLETEBOX (integrated with FilterExpression)  insted of the TEXTBOX for filtering in riadgrid. 

It's too tedious adding a custom filter template , persisting and restoring filter values after postbacks, build the filterexpression manually etc.

I'm aware the checkList can provide similar functionality but it't not so clear,  intuitive, ergonomic and easy to use for current user.

Regards,
Ángel.