AG is widely known to be bad at fitting, because they're more interested in sales and margins, than what will actually make you better, and the people in there will likely know about as much as the average Joe, who isn't a pro.
Ross at the Muni knows his stuff, he's a pro and runs the shop, and he's been using the tech/ launch monitors for years too, which is crucial with fitting.
Don't just pick what goes the furthest, they probably go further because the lofts are stronger, and stronger loft = harder to hit due to D-plane and spin axis. Don't fall into the stronger lofts trap, that catches out 80% of golfers.
If you can get finance in a golf shop, you can probably get finance with your bank too, and there would likely be little difference in the final sums paid. If getting new clubs you're likely spending £1,000, so it needs to be right, don't try and skimp £50 and end up with something with a bad lie, length or grip size, or something which goes miles, but also goes miles right, into the bushes.