More information here:
https://www.macrumors.com/2020/03/24/apple-releases-macos-catalina-10-15-4/
they end the article saying it will probably be the last 10.15 update before 10.16.
“One of the last updates”, to write it down correct. 
It’s being reported today that the macOS 10.15.4 update has critical issues.
https://www.macrumors.com/2020/04/06/macos-10-5-4-kernel-panic-crashing-issues/
Thankfully I’ve held off and am still on 10.15.3.
Surprisingly, my recently purchased Mac Mini (2018) with Catalina has been generally very stable, aside from the asynchronous colour picker that is.
Note: I run both 2019r1.1 and 2019r3.1.
Ive been waiting for one that doesnt.
Looks like it may be 10.16 then…
Yup, wont be updating my older Catalina test machine to it, and by no means will it be getting anywhere near my regular work machine which is still on Mohave.
Catalina is the Apple’s Windows Vista. https://www.theregister.co.uk/2020/04/01/apples_macos_catalina_ssh/
I have elected to upgrade to Catalina, including 10.15.4. No issue so far.
I rather have exactly the same system version as my customers.
Vista was WAY worse than Catalina. It was a deep, intense, utter failure, with illusions of grandeur, and the elegance of a pachyderm…
BTW, it was supposed to be a Mac killer 
I’m still running Mojave with Catalina in a VM.
I do prefer Anthony’s approach. Or a separate test machine if you can have such luxury. 
I will be upgrading soon(ish), but for now I’m happy to spend time testing in the VM.
I always wait the last stable one of a series. Not an early adopter. VM fan.
Can you share with us the specifics of that? How you set it up? The reason I installed it on my daughters old laptop rather than my own machine to start with was because I had read about issues even installing it on external drives that it made changes to the internal drive format even if that wasnt where you were installing that made it impossible to reload back to an earlier version. Rather than risk such a mess I opted to run my tests on one of the oldest machines it still supports 
But would rather have it in a VM here on the same machine with me.
I’ve had no issues. I use VirtualBox on Mac, so there are some extra steps and it’s likely not as fast as it should be. I’d recommend going with Parallels or VMWare. If you use either of those, it’s probably a very simple install process.
separate bootable drive works well
I can boot everything from 10.10 to 10.15
Never had one second of issue with such a thing
I did have to reinstall catalina a few times on external media due to the drive partitions getting corrupted but never had any issue bouncing back and forth between the internal and external bootable drives
I prefer the bootable drive approach as VMs never ran smoothly for me. I can confirm that it’s possible to partition for Catalina and still use the drive.
There are certainly some trade-offs when using VMs. Performance being the primary one, but I’ve never had any actual issues with my VMs once setup.
Thanks so much you guys, Ive overcome my fear then and will install it on an external drive. From that I expect I can boot into virtual box or boot the machine natively off it and switch back and forth.
I use VM’s for quick and dirty tests
And most times that sufficient but there are some things that a VM wont show you
And thats when a bootable drive works well
Being able to do either is useful as heck