Too many horror stories about service companies on group deal sites. I personally avoid any kind of service company. Look at the deals for lawn maintenance, animal removal, roof repair, etc, etc. So many fails, in particular trying to get an appointment. Not worth the risk, just go with a quality company that you know has good reviews from friends or people you know.
there is as much shadiness in the duct cleaning industry as anything. find the marketplace hidden camera piece (eg guy sitting in the basement doing nothing). Lot of cheap offers to get them in and tell you you require more spending.
its very different what the cheap ones are doing vs reputable places putting in the required time. and very controversial as to whether there is any benefit anyway.
$145, through a group deal where the deal site is taking a significant cut isnt paying for much that should take hours. When its not like a restaurant taking a hit hoping to make it up when you keep coming back you need to be very skeptical.