If your current farrier is good and you are pleased with his service then no, I would not switch just because the other guy is $10/horse cheaper.
I also would not take the word of all those other farms--big farms or small farms. At the very least I would want to go to some of those farms--at least one of them, if they have a number of horses I could look at--and check out his work for myself. Or, I would have him come & trim my horses once...or at least trim 2 of them...and see what I thought of his work. Thing is, I have learned over the years that different people have different expectations when it comes to farrier service.
Some owners aren't all that interested in whether or not their horses are correctly trimmed--either they just don't bother to pay attention, or they don't know what is or isn't good farrier work, and so as long as their horses get trimmed every 6-8 weeks, they are happy, and will say that their farrier is wonderful & does a great job. They maybe don't notice that the heels are left too long, or the angles are wrong, or the foot is crooked.
Over the years I've had people tell me that so & so is just a fantastic farrier. Then I've tried the guy for myself & been extemely disappointed in the results. I've been at shows and farms where I was able to size up the trim job on other people's horses--and while they're telling me about their fabulous farrier, I'm noting that the horse's feet are each at a different angle, or the horse is trimmed crooked...things like that. So, I never take anyone's word for it--I like to see for myself. And I'd sure never take the farrier's word for it when he says he trims for Big Name Farm--if you ask Big Name Farm you might learn that they had used the guy once & then sent him packing because he lamed 3 horses!! Yeah, the guy trimmed for them once, he isn't their regular farrier--see it happen that way too.