This are the up and downsides of free software. Free software means no money to the creator. as long as the creator can get income some other way, custom work, installation help etc he can afford to maintain a free software. You do not say what Your business is, but are You willing to give away all of Your service for free ?
The constructor errors are usually easy to fix, just google that bit. It is a non maintained software, but it is free. If You have the time fix the broken code.
GJC on the other hand usually makes good extensions, I use extensions from him that I bought years ago and they still work without changes. But if Joomla decides to make large alterations in their framework for 4.x then there will be changes that have to be dealt with. In this case this applies to all designers, not just GJC. The extension will still work after 12 months depending on what VM and Joomla does with their frameworks.
Jörgen @ Kreativ Fotografi