I looked in to them as well but decided against it. For the $, you can buy or even build a similar house of much better quality. They tend to use cheaper materials (thinner sheetrock, cheap cabinets, fixtures, etc. ). I have heard of many issues with pipes freezing under the house, and you have to duct some forced air heat under the house to keep the pipes from freezing (usually PVC. ) I went to a number of sellers, and my opinion is that they were a cross between a real house and an RV you couldn't drive. A lot of the components seemed cheap and reminded me a lot of materials I've seen in average-quality campers and motorhomes. Not the kind of quality you'd want to live with for 30 years, and that's not even mentioning resale. Realtors I've talked to tell me that normal, stick-built houses appreciate in value (as we all probably know), but these mobile and pre-fab homes actually depreciate in value. You're basically upside-down financially with one of these homes.
I would not get one if you can help it. You'll never profit from it, and the potential problems due to poor craftsmanship and materials will haunt you as long as you own it.
I toured a few of these homes and noticed walls that were not straight and square, and drywall cracks everywhere. I asked the salesman about the flexing of the house and the cracks in the walls (this was a brand new pre-fab house). He said that the structure flexes a lot when it is transported, which is why they use PVC pipes and flex-duct for the HVAC. He said that when they bring a pre-fab to a site, the patch and touch-up all the walls before they hand over the keys to the owner. Most places will return to your home to fix cracks for 1 year, after that, you're stuck with it. Scary.
I just bought my house a year ago. While home shopping, I considered prefab homes quite a bit, but after learning a few things, I decided to buy a real house. At least it will appreciate in value, especially with the things I've done to fix the place up. That way I can sell it for some extra $ and upgrade to a better home.