I've been using vidIQ for about a month. There are numerous bugs - for example subscribers never did "sync"; the +7 SEO columns have always been empty, adding competitors was flakey. Support is poor - Joel in particular - and many tickets have been ignored.
Most importantly of all, though, I've "boosted" many videos and my stats do not show the slightest improvements. YouTube's "Creator Insider" says keywords/tags are largely ignored and are behind titles descriptions and thumbs - and tags are most of what vidIQ does.
And finally there's the issue that it's in breech of YT terms (5h). Their channel is approved though, so maybe YT doesn't care in this case, but others have reported widespread channel damage.