[gregbradley]

As far as Lanthanum and FPL 51 combos go Roland Christen did an article on that. Basically that its inferior. I think though that article was referring to doublets.

Marketing blurb is usual to hide the factor a lesser grade of glass is used. FPL51 is the original ED glass and is old. Its really an area of dishonesty where they leave you guessing what type of glass it is. But my rule is if they don't say its FPL53 then it isn't. Also some companies falsely claims fluorite lenses when its FPL53 so there is a lot of lying and innuendo. FPL53 is weil known so they state as a sales point.

FPL53 is now somewhat outdated and FPL55 is now the latest best. My understanding is its performance is the same as FPL53 optically but it has better properties as a glass which I am sure is good for the optician to get a more perfect lens with.

Petsval potentially is the better imaging instrument so long as its well collimated and solidly built. The FSQ106ED has shown how powerful the Petsval design is. As to how good the quality of this particular scope goes you'd have to check with cloudy nights. Another way of checking is do a search on Astrobin for images made with those scopes and judge for yourself, much more solid ground than asking others.

Is the reducer included in the price for the 115? Or is it extras. Do both scopes come with rings? a case or bag?

Focusers vary a lot in practice and are often a weak spot for many scopes even high end scopes. I would check out that well. Also the focuser needs to be a minimum of 3 inches aperture for full frame. Any less and you are dreaming.

Full frame requires 44mm not 42mm so already 42mm is falling short which could mean wonky stars in the very corners. Ideally wider than you plan to use but perhaps that is not very realistic.

I would personally chose the FPL53 scope as all the top scopes over the last 15 years all use FPL53. All other things being equal.
I would personally prefer a petsval over a triplet with reducer if they were close in price and the petsval had no known issues.

As far as 100mm versus 115mm goes its a bit brighter at 115mm but at the end of the day these are widefield scopes. 800mm is a bit long in my opinion. That would be the territory of 130mm scopes.

Faster F ratio is valuable as well. Faster F ratio does put more pressure on the scope to be well built though.
Edit:

Looked at some images on Astrobin. They were Sharpstar 100Q not the ii model. Some were great some not so good. Tendency towards blue rings around bright stars. One image used a Sony A7rii camera which is a full frame sensored camera. Stars were distorted badly for nearly half the image. Not even vaguely capable of sharp stars to the corners. The best images were from KAF8300 sensored cameras which is micro 4/3rds in size.
So if you plan to use a full frame camera unless the later ii model is way better than the original its not going to do it. There were no images there for the triplet. But it has 9 good reviews. I also bought a high end scope from Astronomy Alive and found Cris Ellis to be very professional, truthful and good to deal with. I'd be leaning towards the triplet.

Greg.