AC1200 extender connected to AC1750 Wi-Fi mesh extender

You won't get "full" speed. 

Here's why. 

When single/dual band extenders operate, they have to use the same chip to go router----extender and then extender--devices.  And they can't do both at once. So they're baseline speed is 50% of what they pickup. For example, if you're router is putting out 100mbps but because of distance/obstruction/interference, the extender picks up 70mbps. Then it takes the 50% hit because of being a single/dual band extender. So its only putting out 35mbps. 

And thats just for 1 extender. if you connect another extender to an extender, its going to take that same speed hit. So if the first extender is putting out the 35mbps, again distance/obstruction/interference, the 2nd unit might only be getting 25mbps. So its only going to put out 12.5mbps.  (just using for example)

Thats what happens when you daisy chain extenders. Its why we usually don't recommend using more than 1 extender and if you do need it, to set it up in a star topology where the extenders connect to the router and not to other extenders.