The Logitech K740 has a type of scissor switch that Logitech calls "PerfectStroke". It is constructed like a normal scissor switch -- just bigger, to provide more key travel than other scissor switches: 3.2 mm whereas most other scissors tend to be 2 mm (or less). I really like these myself.
"Mecha-membrane" means whatever you want it to mean. It is mostly used just as a word to sell keyboards, making them seem more fancy than they really are. It does not denote a particular mechanism or category or anything, and has sometimes been re-used to describe ancient types of rubber dome switches.
The Razer Ornata has rubber dome switches, with a clicker in each switch for added noise. Besides the noise, it has diodes for better rollover than other membrane-based keyboards. But after bull**** marketing tactics, Synapse and SoftMiner, I think everyone should boycott Razer and look elsewhere, even when the product looks good. They don't deserve our business.
(BTW. The OP is a cross-post from Reddit)