Michelle, I'll try to answer you here with words, but you can likely find photos on the web that will really make things clear. The Stroboframe QRC-300 is rectangular and consists of two parts, receiver and plate. The plate is less than 0.2 inches thick, though it comes with a "peel & press" adhesive cork and synthetic non-slip pad 1/16" thick that you can attach to the plate's top if you wish. The plate attaches to the scope (or camera) with a 1/4-20 standard tripod screw included with the plate. The receiver part attaches to the tripod head using the 1/4 - 20 tripod screw you've previously used to attach directly to your scope. There are two little red plastic guides on the receiver to direct the plate to properly align in the receiver and when the plate is pressed down lightly it triggers a button that releases a grooved steel spring-loaded angled piece that slides back and is automatically cammed "in" to capture the entire 2 inch side of the plate. The plate and receiver when connected are about 2 x 3 inches and about half an inch thick. The assembly weighs 5-1/2 oz. The receiver and plate are mostly aluminum, but the "capturing piece" is steel, likely for strength. It has an extension that sticks out the back of the receiver and when pushed forward, releases the plate and re-cocks the receiver so when the plate is pressed in again it will snap back into the secured position. The attachment process is quick and easy and gives a fairly loud "click", so you know it is secure. This could be a disadvantage if you were very near a bird or animal, since it could frighten them away. If your tripod is set up, you can hold your scope in one hand and lower it onto the receiver. When you hear the "click", the scope is attached and ready for use.
I'm not familiar with current Manfrotto QR tripod heads, but my previous tripod was an older "Bogen" branded Manfrotto 3063 head. It had a hexagonal QR plate to attach to the scope (or camera). To fasten the plate to the tripod receiver you had to swing back a spring loaded cam spur with your thumb, hold it there while placing the hexagonal plate in position, and then release it to secure the plate and attached scope. It definitely took two hands to do that. Perhaps Manfrotto has more convenient ones now, but that is the only one I have used. Maybe others who have more recent Manfroto models could chime in here. I do know that the Stroboframe QRC-300 is a really slick and easy way to attach and detach a scope or camera to any tripod. It's capacity is rated 6.5 pounds. Hope this helps. - Bill