connorMcclain
That's actually a veteran product, Connor, though this may be your first knowledge of it. Squadron makes two putties, Green and White. The difference between the two is in the fineness of the grain.
Mr. Surfacer is a thick liquid of a putty suspended in solution (best way I can think of to describe it), and comes in three different grades, again, according to the fineness of the solids.
Squadron putty, Tamiya putty, Bondo, 3M, and other automotive putties differ from Mr Surfacer in that they are relatively solid, but they all have the same kind of application and use. You'll find that many modelers take the solid putties and thin them into a liquid with a solvent, like acetone. I use Squadron putty that way. I'll either apply the putty directly to a seam, then smooth it out with a cotton swab dipped in acetone. Or I'll put a dab of putty in a well on my painting palette and add acetone with an eyedropper, till I have a liquid that I can apply to a seam with a brush. I use either method as a way to get putty only in the space to be filled, and to minimize the amount of sanding when the putty cures.
Hope that helps explain a little further!
Brad