upgrade or not ?

Split view is in El Capitan.

One option is to create a new partition (~30- 50 GB) on an external hard drive, install the new OS, and ‘test drive’ it. If you like/don’t like it it, you can then remove the partition. Do a backup before you do anything. By doing this, if you don’t like it you won’t have to go though the revert process.

Check to make sure your applications are compatible.

Application Compatibility

Applications Compatibility (2)

El Capitan 10.11 Compatibility information

Open Disk Utility, select your hard drive (step 1), then the Partition tab (step 2), and select the partition. Using the /// at the bottom move it up (step 3) until the size box decrease by about 50 GB. Select the newly created space and hit the + button (step 4). Name it something and select Mac OS Extended (Journaled) as the format (step 5). Then hit the Apply button(step 6). Download the installer from the App Store and when it starts, point it at the new partition. You might want to make a copy of the installer outside the Applications folder to avoid having to re-download it in the future. Once installed, go to System Preferences/Startup Disk, select the new partition and reboot. Test away.

Most of the negative issues with El Capitan come in 2 forms.

a) they do not like the way it looks

b) they are having performance issues or the system panics

Not much can be done about 'a'

As for 'b' most of the issues that get reported to the forum turn out to be 3rd party additions that the user has installed which do not play nice with El Capitan. Especially unnecessary anti-virus, unnecessary Mac cleaners, and unnecessary performance enhancing utilities (or so they claim).

In a few cases it is adware they have unknowingly installed.

And in a very few rare cases the user just had a system that so under powered and under configured, it had trouble getting out of its own way (plus many of them had a ton of that 3rd party stuff mentioned above).

If you are concerned. Follow Eric's advice and experiment. But no matter what, make a backup. Make a backup if you decide to upgrade. Make a backup if you decide to re-partition and experiment. Backup backup backup.

I upgraded and had no issues at all. the split view is only in El Capitan, so if that is something you want, go for it. Both my Mac Air and Mac Pro work fine and any issues that may have affected some people will probably have been sorted in the recent updates to El Capitan - perhaps the majority of issues were from third party apps that had not been made compatible..