You mean the difference between
SE1900 'Realforce 87U Tenkeyless 45g' and
SE19E0 'Realforce 87U All-45g "EK Edition"'?
I think it's just that the latter has nice red LEDs, and the former comes with lavender WASD keys.
Basically it's ten bucks less for red LEDs! In the Filco world you have to have stupid MX black switches to get the red LEDs
45 g is the same as the centre switches on a variable weight Topre. They're definitely soft and quiet – if you want a loud keyboard, don't get Topre, go for a vintage Alps board
Tactile Alps switches make a wonderful noise, much nicer than Cherry MX tactile switches.