A stock OpenEars grammar will not be faster to return a result than a language model – finite state grammars are just slower to search. A RuleORama grammar may be as fast as a language model. Either type of grammar should return more correct results and exclude more non-matching utterances than a language model. I still don’t really understand the second question, sorry. If I were you I would just test both approaches so you can see the differences firsthand in your app. Remember to test on a device.