There will be a taste and texture difference. How old are these roosters? They may be a little tough, so grilling is probably out. They're great in a pressure cooker (oh, and look into making bone broth - best thing ever!), or in the crock pot. I think some to them in the oven low and slow. They may seem stringy, but that's because they have been out and about, growing muscle. The chickens you buy in the store are raised to grow out quickly and are processed at about 8 weeks old. They don't have the space or time to grow muscles. Oh - and if you process, it's a good idea to let them sit in the fridge for 2-3 days until rigor mortis has passed, so they're a little more tender.