Well some of the cheaper mods do have a few similar features, but I know few mods which have memory presets, preference settings (like boost, soft etc.) and manual TCR to handle every wire you throw at them.....DNA200, Dicodes and Yihi are the only ones I can think of, and they are not even close to the $50,- mark......so I wouldn't say that the $50 mods can do the same.
Also the SX has been very reliable so far.
But I don't (yet) see the advantage of the ML over the M class...the M class is an excellent mod that can do about everything you could wish for in a mod (if you're satisfied with 75w that is, and I am)
Not a 1:1 but close enough for some people.
The IPV D2 uses a Yihi chip to do most of those things. Honestly in terms of TC and such I prefer the D2. Its a good mod.
For my general use, and maybe others as well, a nice vape can be gotten from other mods.
In terms of hand feel the SX is a dream (boy I wish the button was on top, oh wait it is). I love the SX and with the recent sales its a steal at 100$. I do not like the feel of a D2 in my hand but in terms of a vape 40 bucks vs 200 is a tough sell. The SX is a better mod but 5 times better?? Its not.
Thats assuming TC is desired. I passed the TC phase of my vaping awhile ago and the list of 50 dollar mods that give me an equal vape is loooooong. When I am completely honest my CF4 gives me the same vape in a 29 dollar package and this is my beater/worl mod.
Good god has it really only been 6 months that mods have gotten so good that less then 50 bucks does the job??
All this being said if you can afford a 200 dollar mod the SX is a fantastic choice.