I worked at a residential design-build firm for 10+ years. What do you want to know? What would your role be? Do they have architects or designers on staff? How large is the company? Everyone claims to be high end--how high end are they, really? Do you need IXP hours, and if so, can they provide them? 

Depending on where the firm builds, they may frequently have to deal with permitting and neighborhood review delays, which can affect if you'll be able to get on-site construction experience. (From what friends have told me, it is pretty typical in big cities generally.) If you are going to a firm in a place like San Francisco or NYC, I'd ask if they frequently have projects in construction and if you will be able to get site experience.

Here are my 2 cents:

Pro's

- If it truly is high-end custom residential - then in the right setting you can gain proficiency in thoughtful conceptual design and translating a
coherent vision into intricate fun details. 

- dealing with clients who can be very fussy about minor things, learning to gently nudge/guide them towards the big picture goals and schedule . It's very personal for most clients so it's a very different interaction to client boards.

- more architectural design oriented vs. coordination of a lot of building  systems coordination work from DD onwards on commercial/institutional projects

- interaction with design review boards, various permitting agencies - public works, zoning, building & safety, fire etc and learning how to streamline that process

- some limited interactions with consultants so good place to get your hands wet in coordination - it's usually mostly just structural, soils, civil and landscape on residential projects. Other systems such as mechanical, AV/IT are fairly straightforward and simple to coordinate even on fussy projects.

Cons

- not as much interaction with building codes - site accessibility, building accessibility, fire safety, egress etc. If you need AXP hours or need to pass ARE/state supplemental exams - these are a lot easier to wrap up quickly if you've already done a lot of this work on commercial/institutional/healthcare/ masterplanning projects.

- limited scope to learning redlining, coordination with consultants and clash detection on building systems. Consequently less scope to learn about more complex structures/load paths, mechanical, lighting & electrical systems and how some of the codes such as the NEC work. 

- CA/CD work is whole different ball game and very different to residential projects. You need to have a working knowledge of how a lot of these systems work to be able to be a good PM for CA representing your consultants. The leverage play especially the need to have everything carefully documented with no "design criteria" in the drawings is imperative to avoid errors and omissions CO's for example these days on commercial jobs (much more so than 10-15 years ago)

- its often easier to present projects to bigger boards, public officials as they are more used to looking at the bigger picture, project management and how hard approval processes can be (though not always!)

Hope this helps!

pros - you'll wear a lot of hats if the firm is small, contact a lot of govt. officials, consultants, trades, vendors, etc. and get in front of clients. you will also have the opportunity to learn about very fine detailing and millwork. Also, and not less important, you may have a life outside of work.

cons - depending on the clients and the principal of the firm, your design abilities will have to adjust to other people's wants and needs, it takes a while, but it works fine at the end.