Replacing dead air conditioner

[JebLostInSpace]

I have a 16k BTU self-contained air conditioner made by Marine Air Systems in 1998. I had an expert come out to look at it and pronounced it dead (compressor is shot). Now I'm getting quotes on replacing it, and trying to understand what's important to me.

The quotes I'm getting are for a direct replacement, ie the 2020 version of the Marine Air Systems (now Dometic I think?) 16k BTU unit. These quotes are for ~$3100 plus labor to install it. When I do just a generic search for a 16k BTU unit, I can find several options from other brands that are substantially less expensive. As an example, here is a link to a MarineAire one for $1800.

https://www.marinaire.com/Marine-air...QaAmgQEALw_wcB

Is there a reason this would be a bad idea? Is it hard to replace with a unit from someone else? It would of course be nice to be able to use my existing control panel, but is it a big deal to swap it out? Or are these units just crappy? Or are there other parts not included in these listings I would have to get as well that would bring the total price up? Or are these quotes just trying to talk me into something needlessly expensive?

Another interesting thing is this "retrofit" kit, which looks like it's the exact dometic product I would want, but for $1800? It feels like I'm missing something here.

https://ameriprods.com/products/dome...e-retrofit-kit