ex6120 strong enough???

hi, we had the new  fiber optic line and their router installed by our local frontier phone company.  the guy that installed it said if we got a new smart tv in bedroom 

(other end of house ranch) we would need a wifi extender he, told us his house was simular ranch and you could use the middle one (extender ex1620). it does work good but sometimes we loose a program and have to go an recheck or wireless connection which is good??  should i get a more powerful extender.  we do live in a rual wooded area.  thanks