A repair shop is a building with lifts, a parts counter, a front desk and a schedule. You bring the car to it. A mobile mechanic is a technician with a van full of tools who brings the shop to the car. Both can replace your brakes, your battery or your alternator. The difference is where it happens, what you pay for and what you can see.
The honest comparison depends on the job. A brake job, a battery, a starter, a check engine light diagnosis, an oil change: these are mobile mechanic jobs, and the shop adds cost and time without adding anything else. A transmission rebuild, a wheel alignment, internal engine work or body repair: these need equipment that doesn't fit in a van, and the shop is the right call.
Mobile-Car-Repair.xyz's local mobile mechanics will tell you which category your repair falls into during the quote. If it's a shop job, you'll hear that before anyone drives out.