We currently use Device42 discovery, and it's bar-none the best discovery tool I have seen in a while. The only tool that compared was BMC. We have a pretty diverse environment, being a colo ... so, lots of different equipment. Out of the box they discovered about 95% of our stuff, and the few things we needed, we asked support & they built us support for in maybe four weeks.
My team and I really like how easy it is to use. We've been working to automate our build process to both pull data from device42 (specifically, free IP's), and then populate it with the newly built data as well. Our team is already spread pretty thin so we didn't have the man hours to configure a complex tool.
Full disclosure - I did a trial of Device42 for ~8weeks so when we decided to put it in production, I was already pretty familiar with the software. That said, I think I've only needed one (hour long) session with an engineer in the two years we have had the product -- and that was to go over some new feature changes. They also have a pretty complete API, and a lot of scripts, some we've used as is, other ones we've modified and use regularly now as well. In addition to integrating with ServiceNow, they also integrate with a bunch of other products ... (half of which we already had in place) so that was a plus.
All in all, still loving it -- that's my two cents! Hope it helps .
