I don't think I've noticed a difference in my frozen seitan. I usually make my own though, and it goes really quickly! If you have Bryanna Clark Grogan's cookbooks, she has really good seitan recipes www.bryannaclarkgrogan.com
I like to slice it thinly, dredge it in some flour and brown it in some olive oil and make a nice sauce for it, with spices, wine and veggies. Serve it over rice and yumm.