I recently purchased a Samsung T5 500GB SSD, to use as an external startup, running High Sierra, but didn't notice any boot up speed gain, ran Black Magic and the results are poor, see attached, I ran Black Magic on the HDD just to check and results were as expected (good for the HDD), so tested the T5 on my MacBook Pro and the results were optimal, is there something I'm missing on my iMac setup ??
It's limited to the slowest part of the chain, USB2 is slow compared to USB3...
https://www.macworld.com/article/2039427/how-fast-is-usb-3-0-really.html
I used Firewire 800 external SSD & it was only around 80 <B/s but was fairly fast in booting & running from it.
Simply said, any iMac prior to 2012 will not benefit at all by adding an external SSD. On 2011 and prior machines, the SSD installed should be internal to get any type of speed advantage.
The Late 2009 iMac has USB 2.0.
The MacBook Pro has USB 3.0 or USB-C.
Late 2009 iMac 21." External SSD very very slow
