Silk Touch produces custom drops and silk touched block, regardless of whether "dropsilktouchalways":true, is set to true or false.

"allowsilktouch":false, prevents the block from dropping but in turn means silk touch won't have affect on the block.

Basically silk touch either doesn't work or it works and also drops the custom block drops, which isn't ideal.

Take a look for a simple Redstone example

#10 (comment)