Tiger 0.6 mm.
SPI depends on the project. 2 mm is too tight, if you ask me, even for small goods like watch bands. You might need to use Fil au Chinois 632 or even 832 with those chisels you got. (https://www.rmleathersupply.com/collections/thread-sewing)
Check out this reference: https://www.ianatkinson.net/leather/leatherguide.htm#stitching
Ghostery prevents me from accessing your link, but my emphatic advice is that you don't waste your money on crap. Whenever I hear 'cheap import' it usually means Chinese-made by the lowest bidder—actually, scratch bidder, because the junk is so terrible that they didn't even qualify to bid. If you want inexpensive and still good quality and reliable, get yourself a pair of Seiwa chisels from goodsjapan.com:
https://www.goodsjapan.com/seiwa-diamond-leather-stitching-chisel-leathercraft-pricking-iron-tool-2x3mm/a-19396
https://www.goodsjapan.com/seiwa-diamond-leather-stitching-chisel-leathercraft-pricking-iron-tool-6x3mm/a-20901
That's what I have for my 4 mm spacing: a two-prong and a 6-prong: they do the job flawlessly.