Jabeile, buying from straight razor designs would far outweigh getting one from amazon. Any of the razors you linked would shave the same. There might be slight differences between the 5/8 and 6/8, but the difference would be so minute your father would not be able to notice them.

One of the most important parts of learning to shave is starting with a razor sharpened to shave ready condition. With straight razor designs (SRD) the razors come professionally honed by one of the best in the business. If you buy from amazon you have no such guarantee, even if it is advertised as shave ready.

Secondly, SRD has an amazing offer where they will give free sharpenings for life if you buy from them this holiday season. Given the quality of sharpening they offer, this is an amazing deal. Usually a razor will need to be sharpened every few months, and sending it off to be sharpened usually runs about 20 bucks plus shipping. To have the best sharpeners out there do it for free every time is an incredible deal.

Please, do your father a favor and don't buy from amazon.

As to your strop question. The strop does not need to be made by the same company as the razor. Ruprazor has some nice strops worth looking into if you don't want to spend too much.