Is there anyway to tell If my iMac has a blade installed or and SSD?
First, about terminology. There is not an "either/or" equivalency. "Blade" is one of the physical form factors (shape) that a solid state drive may have; "SSD" is the storage technology inside, regardless of form factor.
What drive does your iMac have now? There are suggestions from some vendors that an iMac must be fitted with either a factory SSD or a Fusion drive to able to accept an internal SSD upgrade; otherwise the blade slot is not enabled.
If you now have a straight mechanical hard drive, a fast external Thunderbolt 3 drive would be as fast as an internal SSD. Best of all, it would avoid the risks involved in opening the computer case
The factory SSD and the tiny one that is part of a Fusion drive are blades that fit a socket on the 2017 models' logic board. However, are you aware of what is involved in opening an iMac made after 2011? The case is sealed and there is a high chance of causing irreparable damage in attempting to open it.
If you do "About this Mac..." from yourApple menu and click the "Storage" tab, you can see the kind of drive you now have in the label under the drive icon:

"Flash Storage" in the image indicates a factory SSD.
"Fusion" means there is is a tiny SSD and a larger mechanical hard drive chained together to be a hybrid drive
"SATA Disk" means it is a pure mechanical drive.