does this have a standard 3/8 threaded connection too or does it have to be quick connect? If so is the a qc to thread adapter available?

Quick connect pressure fitting. I didn't see any threads. Works great for my Manitowoc ice machine plastic lines.

Will it fit the apec top tier 5-stage ultra safe reverse osmosis drinking water filter system (essence roes-50) the top filter above the membrane?

All depends on the inlet and outlet style and size of fittings. 1/4, 3/8 quick connect , barbed or threaded?

I want to upgrade a 1/4" filter and line to 3/8th. How would I adapt the input of this filter to 1/4"?

With 2 reducing straight push to connect union and 2 pieces of 3/8” tubing approx 1” long UNION : Brand: YZM Part#: 8541998658 Model #: 8541998658 Connect 3/8” piece of tubing to 3/8” filter fitting, connect the 3/8” end of the union to the 3/8” piece of tubing, connect 1/4” tubing to 1/4” end of the union

Why do the photos show icf-10 when this is supposed to be 10q38?

Unfortunately, the stock photo is of an ICF-10 with 3/8 fittings. Probably an error on the graphics team. We have replacement photos in the works, hopefully, to be changed soon.