Pretty much. As I understand it, the 1.5 and FF are basically identical with the exception of parts values, which gives them a little different sound. The mk1 was introduced as a 3 transistor fuzz, then a series of TBs were discovered to only have 2 diodes later on and chronologically that happened between the mk1 and mk2. The 2 transistor version (1.5) wasn't actually advertised as a new model or anything at the time... it was just another Tonebender for all intents and purposes. Then as you progress to the 2, 3 and 4 it deviates a bit further away from the original schematic.
I sort of feel like the 1.5 and fuzz faces have a bit of overlap. I've been doing a bunch of research on Mk1 options. Right now I'm leaning towards this: https://www.joedocmusic.com/jdm-pedals-elektrika-customjdm-pedals-elektrika-custom-tonebender-mk1/
I also am a little intrigued by the mk4 after hearing it on the this TPS video with Josh Scott. 42:00 into the video they get into the Mk4. https://youtu.be/UrJDtSolEI0
I paid for Boost premium for Reddit a long time ago and will do it again just to support it here.
Every time I see a Splinter I get the urge to buy one just because they're cheap. I don't really need another Rat, but I sorta NEED it.