I've loved Swann Morton for years ever since using the old school burnt orange model makers blade holders they made for many years as a kid. I recently came across the "retractaway" blade holder in a makerspace toolbox and was immediately impressed with how it felt in hand and secure the retracting mechanism was. So I ordered one and have had it for a couple of weeks. It's a pleasure to use and after years of scalpel holders in toolboxes that may or may not retain their cap/cover its nice to know this is safe when chucked in a box.
Not much to say technically apart from its only designed to be used with a small range of blades. 10, 10a and as luck would have it 11 and 15, the latter of which is my favourite and is the fitted blade in the image. It has 3 idents on the retracting mechanism, closed, half open (the working position) and fully open (the position for swapping blades). Retention is great albeit with a slight bit of side play in the blade assembly. In usage though this rarely causes any problems and it's capable of very fine work.