The sales assistant was correct to a small degree. However, that can be true of cloning from any drive to another drive, be it HDD to SSD or HDD to HDD. The reason is Windows installations will usually slow down over time due to repeated tweaking and modifications. A clean reinstallation will often speed things up.
However, if one's window installation is working just fine, then cloning it from an HDD to an SSD will not result in a slower installation of Windows compared to a clean installation. If upgrading an HDD in a laptop or a commercially built desktop, getting drivers for a reinstallation could be a chore. Also, a clean reinstall can be a lot of work, especially if one has a lot of programs or has heavily customized windows. That's when cloning makes more sense when upgrading from an HDD to an SSD.
I used Macrium Reflect to clone the HDDs in two notebooks to SSDs without any problems at all. With each notebook, I plugged the SSD into a USB dock, ran MR, ejected the SSD when MR was finished and removed it from the dock, then shut down the computer and swapped out the HDD with the SSD. After rebooting, I had to reletter a partition, then everything was all hunkydory.
When making the clone, since a drive letter can exist only once ona computer, all the drive letters on the clone will be different. Don't let that bother you. When you swap out the drives the System Reserved and C: partitions will automagically revert to their original designations. If you have any other partitions on the drive, you can always change the drive letter back to the original one in Disk Management.
I don't know why you would want to use an SSD to backup an HDD. After cloning the HDD to the SSD, I would swap them out and use the HDD for the spare. The SSD will be amazingly faster than the HDD.
Also, cloning is not the most efficient way to backup a drive because you can have only one clone on the backup drive. Imaging is much more efficient. Because images are compressed, they take up less room on a backup drive and you can have more than one image on the backup drive (this allows you to go back to different points in time, much like System Restore does...when it works). That said, cloning does have the advantage that, if the drive in your computer croaks, you can swap out the the drive with the clone and be back up and running quickly. However, that also leaves you without a backup until you can make another one.
I only image the boot drive (which has the OS and programs only) in my desktop rig. I use a folder/file syncing program (
FreeFileSync) to backup my data drives. While imaging and cloning are the only way to backup System files (OS and programs), they are too inefficient for backing up data since everything gets rewritten to the backup drive each time you update the backup. A folder/file syncing program, when set to mirror mode, will compare the data drive to the backup drive, then copy over any new or changed folders and files on the data drive to the backup drive and delete any file on the backup drive that are no longer on the data drive, resulting in what is essentially a clone. Since only new, changed, and deleted files are dealt with, backup updates are much faster.
I do things a little different on my notebooks. I only use my notebooks when I'm traveling and as a backup for when my desktop ring is down. Since any data in the data partition on the notebooks are also on my desktop rig (I can also download the data from my Carbonite account if I have a secure internet connection), I don't worry about backing up the data. Instead, I have two backup drives for each notebook. I keep a clone on one backup drive so, if the drive in the notebook dies completely, I can just pop it into the notebook and be up and running in a few minutes. The other backup drive has images of my System Reserved and C: partition (the data partition is unlikely to ever get messed up and, as stated before, I can retrieve the data from elsewhere if needs be) so I can restore them if they ever go wonky on me.
Btw, much, if not most, of what I know about backups, etc. I learned here at Seven Forums so that thanks should include the folks here, some no longer with us 
