Using the Tunisian joining method for crochet squares can certainly make a nice joint to be seen or a hidden join. It seems to be a bit faster and I joined 8 squares at a time with these squares. I think if I had a smaller Tunisian hook than the 4.00mm I have on hand, I would have opted for a smaller one. You can see more on the Tunisian joining method here, with the original learning link I used. Next time I will use a different colour for the joining method so as it can be seen much better, the photo's do not do it much justice.
This is the joining side.
This is the opposite side to the joining side.
This is the size 4.00mm Tunisian hook I used.