I have a laptop with 8gb ram, 1Tb HDD, i5 7th gen running windows 10 and Ubuntu. Right now I'm using windows 10 as my primary OS, I'm simply addicted to the gestures especially the four finger swipe to switch desktops. I have been thinking of adding an SSD to the mix and my budget only permits a 120gb M.2 or a 250gb normal ssd.

The advantage with m.2 is that I can keep my HDD and boot my OS from the ssd and maybe install my IDEs on there but with the other ssd I'm gonna have to take my HDD out and use it as an external.

I read somewhere that 250gb above SSDs are the ones worth spending money on and that the 120 and 250 doesn't justify the price or life.

So my question is, should I go for an SSD? and if I do which one to go for m.2 or the normal one?