I know that the product is good but I have some doubts about projects that do not have a open issue tracker and that do require you to use the mailing list.
The only thing I was able to find was https://admin.reportlab.com/mantis/project/core/tracker/ and is more than one year old.
Even if the license of the product is GPL, the read access to the source control repository is only for partners (paying at leas 2000 EUR/year).
Also for many modules the source code is not available at all to not paying customers - And if I'm right this is a clear VIOLATION of the GPL license.
Also even the software is quite stable the project seams to have a quite small community contributions, maybe just because of the products 'special' business model.