In a word, no. LL beans have been out for several years now, and there is more than enough proof from yield trials, and anecdotal evidence from farmers raising them, to dispel any notion of yield drag. Truth is, they are quite competitive yieldwise with RR, and sometimes better. I wouldn't be a bit afraid of LL beans. Just make sure you have all your ducks in a row, production-wise, which would be true of raising any bean.

JDH