Rest of house is concrete block, but the addition looks more like a manufactured house in terms of materials.

As far as the insulation goes, I would check with the manufacturer to see about mixing, but at first glance can't see why it would be much of an issue, although it may be difficult to figure out what your R value is.

Does anyone have any suggestions in regards to manufacturer?

No one needs that reputation of being accused of the F-word, especially in these times.

The house I was looking at and the rest of the ones on it's street, are "normal" SFHs, but then there is this manufactured home across the fence.

A good reputation is not made in a day.

. :) if only a couple of hundred difference more use reputable contractor...i'm still trying to find guys that put in an AC unit in for me

This is how realtors earn their reputation as "scum" (another BP thread).I'd rather deal with used car salesmen than realtors.

I'm an electrical engineer and currently work for a company that designs unmanned aerial vehicle targets.I also dabble in all sorts of other things...LED manufacturer investing, development, syndication/private equity, etc.

.* Approx rental share in area, vacancy rate from reputable prop manager, area unemployment rate.* School reputation for family-sized units.