Personally, I would just buy the larger size of the Bloc Loc. I don't see a need for all of the smaller sizes, especially in terms of storage. I like to reach for just a single custom ruler, not rummage through a pile. The one advantage I see to purchasing the smaller rulers is that I would not have to be quite as careful to find the correct cutting line on the ruler. As I get older, I notice I prefer to have things as visually simple as possible. However, what I would do if I were going to be cutting lots of the same size smaller HSTs with a Bloc Loc ruler is use a small strip of blue painter's tape to mark the squaring-up lines I want to use.
Be aware that there are two versions of the Stripology ruler. The one I have is their first one, which is the larger rectangular version. In my opinion, it has a design fault. The cutting slots are too short, so that I often cannot cut all the way through the selvedge edges when using it. With their newer mat, the Stripology Squared, they corrected this and made the slots nice and long. However, it is a smaller mat so you get less cutting slots. Personally, I think the Squared is a much better purchase.