All brands are different, so it depends. Sometimes you can save $ by buying through your plumber b/c they save money on the product, but the labor is what you pay for. If you have to have it installed anyways, it’s best to go with a plumber, unless you want something more specific than what they carry.
Absolutely not I am a general contractor and I know from experience like any other product you buy it from The Big Box store And its cheapened because they pay less for volume so they get a lesser product ie plastic drains and plastic internal parts vs Metal no warranty if it goes bad it’s the homeowners problem and or you the contractor… a good plumber will stand behind their warehouse fixtures and not the box stores… best of luck