It is usually cheaper to print 4R at photo shops.
The cost per print usually goes down as the cost of your printer goes up. And photo shops use seriously expensive printers, ranging in price from under RM100K (analog machines + digital adapter) to RM400K++ (fully digital machines). Even factoring in their profit margin, they can still offer 4R prints at lower price than you can get printing at home.
It's just more convenient to print at home, if you have just a few pieces to print.
The quality of shop prints varies. Depends on how well they maintain the machines and chemicals used (if they're using the wet silver hallide tech). It could range from somewhat worse than a good inkjet home printer, to many times better than the very best home inkjet printer. Newer dry machines don't have this problem, but the cost per print is higher. IINM all the Fuji machines have been inkjet for a few years now, but of course they are nothing like your home inkjet.
The skill of the operator also comes into play. Is he lazy, and simply put the machine in auto mode, or does he adjust the exposure and colour balance of each picture, as well has how skill is he at this.
To know the quality, just go to the shop and look at the photos there. You can tell them your concerned about the quality and would like to see some samples. Or you just stand around pretending to look at the products on sale, and then sneak a peek when another customer collects his photos. Most people tend to flip through at least some of the photos, just to make sure they've got the right set. You can make some comments to the customer about the photo, and he might show you more.

Between 5R and 8x12, it's probably cheaper to print at home. Because photo shops call these "enlargements" and tend to charge a much higher price. Larger than 8x12, most home printers couldn't print them. Most photo shops can print at sizes up to 6R, 8R, or 12R. For larger sizes, they send it to a central lab. You'd know this cause what they can print right there, can be ready in 30 minutes, but the larger sizes takes a few days.