As has already been said, there are many different types of High Speed Steel. Specifically, not all tool steels are HSS. M2 HSS has a very specific alloy formula with very tight limits on each alloy element. Heat treating M2 HSS is very complicated and cannot be accomplished by the average home metal worker. Much of the bulk M2 HSS readily available in bar stock is un-heat treated, meaning annealed and soft. Metal cutting bits like we use for hollowing are usually heat treated when purchased.
M2 HSS from Sheffield is quite different from Chinese HSS. The quality control is dramatically different in China than in England. Sheffield steel has a long history of high quality steel. If you grind Sheffield steel, you will see uniform dark orange sparks. If you grind Chinese HSS, you will see brighter orange sparks with some of the "sparkler" type sparks as well, like you would see when grinding plain Carbon steel. Chinese HSS is much coarser grain structure with lots more impurities and is usually softer. Sheffield steel is very clean and uniform in formula and grain structure. This is why particle metals have been such an improvement. The powder they are made from is extremely fine, and every particle is exactly the same as the other. So when the powder is heated and compressed into solid stock, the resulting material is very uniform and consistent. Not so with the Chinese steels. Many of the higher end turning tools are now made from particle steels. which is part of what makes them so expensive-the steel production process is very expensive but results in a superior steel. Even hand plane blades are being made with particle steels now. The extremely fine grain of these steels is part of what gives them the abilty to take and hold a very fine edge.
Just this past Saturday, I was teaching a bowl turning class. Our club has several Ben's Best tools. I showed the class the difference in steels by grinding a BB tool and then grinding one of my Artisan (Henry Taylor-Sheffield) tools. Very visible difference in the resulting sparks !
I do not claim to be an expert in steel, but I have read a lot on the subject. I also spent several years in the powdered metal industry working for Pratt-Whitney as a metallurgical tech in quality assurance doing chemical analyisis. I actually started out on the furnace and worked my way up to the QA lab. That was after getting my B.S. degree in Biology (not meatallurgy I know, but lots of chemistry and physics).
You can find the actual alloy composition of M2 HSS by searching the internet. It's really quite interesting.
So, my long winded answer to the original question is No, not all M2 HSS are the same.