I am 100% on board with Roger here. Discussions of glass in the absence of a complete OTA design, especially with regard to color correction, will bear little fruit. FPL-51 based OTAs can have excellent color performance, depending on the mating glass, design and manufacturing quality. The same can be said of FPL-53.
I think the one thing we can say definitively is if a scope designer/manufacturer starts with FPL-53 glass, they have an easier job of it making a well-corrected OTA for any given focal length.
Both materials can be used to make a superb instrument.
When one is talking about affordable doublets like the StellarVue Next Generation Nighthawk, my experience is that the color correction is very consistent with the differences between FPL-51 and FPL-53. With the common mating elements, FPL-53 offers about 1.8x the color correction of FPL-51 and this translates into much less chromatic aberration seen at the eyepiece.
FPL-51 based doublets I have owned: WO 66SD, AT 72ED, Astro-Tech, AT-102ED, Looked through: Orion 110mm F/7 Premium
FPL-53 based doublets I have owned: WO Megrez II FD, AT-80LE, Orion Eon 120. Looked through ED-100.
The 120mm Skywatcher is testament to what can be done with quality and/or glass choice. At 120mm F/7.5, even though it's FPL-53 it ought to show chromatic aberration but I don't see it even on Venus..
The scope in question, it's not an ED-80 when it comes to color correction.