As the link to the web page does not state the type of ED glass your post is purely conjecture.
Not that it matters, as according to the Abbe numbers for both types of glass they are quote close in performance.
I have a 110mm ED that uses HFK61 and it is a great performer...
This is how I see it:
- At that price, it's unlikely it is FPL-53. And in general, if it were FPL-53 or something similar, they would mention it.
- Actually they're not that close. FPL-53 can offer about twice the color correction of FPL-51. I have owned a number of HFK-61 doublets, they're good, much better than an achromat but certainly chromatic aberration is visible without much difficulty. The AT-102ED, I purchased 10 years ago was definitely colorful. One night I made a comparison with the NP-101 on Venus, the 101 was color free, the AT-102ED definitely showed purple fringing. The 110mm F/7 I looked through one evening did a good job.. Great is somewhere else.
- In any event, this is F/11 and not F/7 so it should be quite good. And there is more to a refractor objective than just color correction. Hopefully Thomas will have a stunning performer on his hands.