Hard to know where that set comes from but almost certainly "offshore."
Reviews on Midway USA are mixed. On the principle that "life's too short to buy cheap tools" I'd go for the Brownell's drivers. They're known to be good quality, plus you can get exactly the bits you need. I've only ever bent one bit and that was a thin one, trying to turn a very ornery screw.
If you dig around on the Brownell's site (ie
here) you'll see that the first 3 digits are the blade width in decimal inches, and the number after the dash refers to a particular blade thickness. (There is also a "445- " series which doesn't follow the decimal width rule.) You'll need a 340-5 for the front trigger guard screw, and various -3 or -4 for the others.
For the butt retaining screw, you're on your own. You need a honking long screwdriver with a very big blade. I made my own from a 16" length piece of square tube with a piece of 1/8" (I think) flatbar set into and welded on one end and a piece of 1/4" rod welded to the other to form a t-handle.
You may already know this, but if you do order form Brownell's, make sure they can ship USPS if it's coming to Canada as UPS etc. will rape you on brokerage fees. (If you live near the border you can use a "just across the border" UPS/Fedex depot for non-USPS orders.)

Stuart