For those brave souls who want to upgrade to the first iteration of Catalina, read Review: macOS Catalina 10.15 is what Apple promised the Mac could be, and is a crucial upgrade.

Personally, I never upgrade to the first version but this time, I also need to figure out how to replace Entourage 2008, which won't work in Catalina (it's a 32-bit app). I have some ideas, but the main problem is that Entourage accesses my ISP (Spectrum) via a POP account and, when I set up Outlook 365, it became an IMAP account, which I don't want. I'll contact Spectrum for their advice. Then, I have to have a way to preserve wanted emails from Entourage. At any rate, I'm not yet ready to take the plunge.

I'm not moving up until I get my Safari extension situation resolved; I'm running two important ones that I'll lose in Safari 13.

And for all you Little Snitch users:
"The latest release [of Little Snitch} updates macOS Catalina support.
macOS Catalina Note: Please upgrade to this version before you upgrade to macOS Catalina!
On Catalina, system apps have been moved from /Applications to /System/Applications and the paths in rules must be updated. If you upgrade to Catalina while a previous version of Little Snitch is installed, rules for system apps are not updated."

And you can change your mind. Spotted this on Macworld.com:

"Have you ever installed a software update only to discover that it has broken other software you depend on to do your job? Catalina adds a new feature that takes a snapshot of the system disk just before applying an update, and allows you to restore your Mac to that state via macOS Recovery. (Restart your Mac and hold down Command-R to boot into macOS Recovery.)

This is a clever use of the snapshot feature of the APFS filesystem, but it takes up a lot of disk space (since your drive has to save very bit of your pre- and post-upgrade Mac). Snapshots are only retained for a day, and if you don’t have enough free space available they won’t be available at all."

It may not take up as much space as you think. Normal APFS snapshots include only the effected data sectors — not necessarily complete files. In fact you cannot restore a single file from any snapshot, you have to restore the entire volume to the state it was in prior at the time the snapshot was taken.

One other thing to be aware of in Catalina, the boot drive will have at least three separate volumes

1. Recovery Drive <~1.06GB>
2. Drive name <10 to 20 GB>(this is the boot system)
3. Drive Name - Data (everything else including apps data files etc.)

As far as I know regular snapshots are only available on the Data volume so the installer snapshot would appear to be a special unique case.

The observation I quoted above from Macworld.com was intended to share how one could downgrade from Catalina to an earlier MacOS, not to restore individual files.

Early adopters beware: Missing message issues plague Mail users in macOS Catalina

Here's another precautionary article: Minor Lightroom and Photoshop bugs pop up in macOS Catalina

I upgraded to Catalina 10.15.2 today. System Preferences has a different appearance as does Mail. Mostly, it was smooth. The process took quite a bit of time because I updated my three clones before installing Catalina. That took about 25 minutes and the installation, including downloading, took about 40 minutes.

I went through my Applications folder and deleted all apps that had an X through them, meaning that they were incompatible (I knew about most of them before because they were 32-bit). I then updated OnyX, Cocktail, Tinker Tool System, Adobe Flash Player (no snide remarks, please!) and Ejector.

So far, so good.