PE/VC-backed bait-and-switch takeovers of "open source" projects have cost me a significant amount of time and money over the past few years.

My rule of thumb now is that I now consider any project that has a pricing page OR requires copyright assignment/CLA to a for-profit company to be effectively proprietary and just using open source as a marketing technique. That doesn't mean I won't touch it, but like with proprietary software, I'll evaluate it against the risk that the price will probably be jacked up in the future.

The important part is the contract the company signs for you. Contacts generally are enforceable in court and lawyers know of standard provisions for weird situations (what if the company goes bankrupt)

QT has contracts with KDE around the open source version which gives KDE peace of mind. I use QT in a commercial product - we have some useful contract terms with QT that are not public and I can't talk about them.