I have the D5 and love it. Like most new technology, it takes a little while to get used to it so I'd recommend trying it around the house first or on an inspection where the homeowner isn't hovering over your shoulder.
Measuring a rectangular 1 story home would probably go faster with a tape. However, it really comes in handy for the unfinished utility room where most people have boxes stored and it's difficult to walk around. Point a laser beam at the other side of that room has probably kept me from breaking a leg.
I'm looking for a model that you can use for the exterior measurements. I have heard that some are difficult to read in the sunlight or you can't see the laser if it is a long distance. Do you use yours on the exterior?
I have the Leica A5 and would not trade it for anything. I would not go anything less than the A5 however. I love how I can take four measurements first before I transfer to a sketch. Also, I frequently use the site/scope to take a measurement since sometimes in bright sunlight, it is impossible to 'find the spot'. Having the crosshairs makes it easy.
Cory