GREAT! Replaced my HDD of a MID 2011 iMac 27" with a Crucial SSD 1 TB in 15 minutes (two people).
Performance is 100 to 1, this is really like buying a new iMac, but at 10 % of the cost.
Prior to replacing the HD I made a TimeMachine backup of my iMac and created a USB-Boot device for OS X Sierra.
After installing the SSD drive, boot up from the USB device and make a fresh install of Sierra. After this, connect your TimeMachine backup device (i used a 1 TB external USB HD) and use the Migration-Assistant from the Utilities Programs to restore the User/Apps/Data files from the Time-Machine Backup. The restore took about 5 hours (600 MB) because of USB 2.0 - so be patient.
This way you will end up with a FRESH IOS INSTALL and all your mail/settings/data/apps/fotos... from your TimeMachine Backup.
I absolutely recommend this upgrade because of the exceptional performance gains when using fotos, garage band, motion, final cut pro x, imovie - BIG SMILE!!!
...just do it!...
