I have 3 stout faucets. 2 stainless like what you have from the beverage factory (got them from northern brewer) and 1 actual Guinness tap from a bar (ebay) that is brass. They both work about the same, I do not like the plastic spout on the Guinness one, just feels wicked cheap and looks cheap. I think you could buy a steel spout and just swap it in though. I believe the brass Guinness one I have is the same as the brass one you linked (aside from the tap handle). Something to note, I'm not 100% sure that stainless stout faucets are all steel, I think part of them are chrome but everything that touches the beer I think is steel.
I have a portable kegging setup and use the brass on that, the 2 steel are on my fridge.
They come apart the same, pour the same, use the same o-rings. In a blind test you couldn't tell them apart IMO.
As far a brass vs stainless, is it worth the price? What is the real difference? I'm very much a long term planning kind of guy. Spend it once and never worry about it, I buy 50 year caulking for double the price, sort of silly I guess. So for me I never want to doubt or worry about my gear. To me that means I go all stainless steal, it's "the best" and should never be a problem. Would I ever notice a difference? Probably not. Would it bug me if I spend $60+ to brew some wicked special stout and I don't have "the best" setup to serve with? Yep, it sure would. Should it bother me? Nope, it shouldn't but it does!
You can also look at it this way, I'm sure brass is fine, but if they are the same price would you ever pick brass over steel? However, my real Guinness tap is from a bar, how many pours did it handle? More then I'll ever put through it. The only piece of reasoning I've heard for steel over brass is steel will not react with anything in the beer, ever. Brass over prolonged contact will react. I'm not sure what that really means but I don't think anybody ever upgrades their steel to brass for anything in brewing.
Anyways, for all practical purposes you can go either way. For me, there really was only one option, steel.
