The 4-Mix blowers are the "4282" series units, so the kit you have shown in your picture is for a BR500,550 or 600 only.
The 4-Mix shafted products all use the "4180" series kits.
On a side note, I would recommend using 2 feeler gauges stacked on the exhaust valve only on the BR product. Not needed on the hand held units.
I have been amazed also at the retail price of some of the parts for a Stihl unit. You would be surprised at how many spare parts that are under $1.00!
I agree however on the flip side that there are some items that are priced sky high!