@washingpowder
The refillable bottles are not much sturdier than the UltraPhase 1/2 bottles. The only real difference is the hole on the top of the cartridge with a cap on the refillable cartridge. As I said before using a funnel is not really any harder than using the refillable bottle with the hole on the top.
The ingredients for UltraPhase 1 and UltraPhase 2 are posted online. Here are the links:
Phase 1:
https://images-eu.ssl-images-amazon.com/images/I/71PpAUDMgsS.pdf
Phase 2:
https://www1.miele.com/pmedia/ZGP/data_sheet/100125572-000-00_UltraPhase2_11997107.pdf
Our family goes through a LOT of detergent due to the amount of laundry. Tide PurClean can be bought in 75oz bottles for about $7.50/bottle when Target or another store has it or cleaning products in the store app with cash back and then combine with manufacturer coupons. That makes it .10/oz. The Miele Ultraphase 1 cartridge costs $19/50oz bottle. This makes it .38/oz. Almost 4x more expensive.
We dose Phase 1 at 17ml. If all loads had 17ml that means Tide would cost 5.75 CENTS per load vs Miele at 21.84 CENTS per load.
Cost per week (50 loads per week)
Miele: $10.92
Tide: $2.88
Cost per year (50 loads per week)
Miele: $567.84
Tide: $149.76
Savings per year with Tide vs Miele: $418.08
Savings over five years Tide vs Miele: $2090.40
This is only for the detergent portion of the TwinDos system. If you add in Phase 2 as well the savings is larger.
As you can see using Tide vs Miele will save the entire cost of the washer over a five year span. I picked five years because we will most likely reach 10,000 hours within the next five years. 10,000 hours is the design life of the W1. So just switching to Tide and using coupons can save you the entire cost of the machine over it's life. It's not an insignificant choice.
Lets look at time savings of TwinDos vs pouring detergent in the slot. Lets assume an average cycle length is 1.5 hours. This means 6,666 cycles in the design life of the machine. If it takes you one minute to retrieve the detergent bottle, measure the correct amount and pour it in the traditional drawer in the washer you will spend 111 Hours dispensing detergent.
If you figure $15 an hour you have a time cost of money of $1665. Meaning if you had to pay someone a decent wage as a maid the cost to dispense detergent over the life of the machine; that is what it would cost. Now we have to deduct off the time to swap a Miele TwinDos bottle. We will call this one minute. Since each bottle, at 17ml per load, will last you 88 loads this means you will use about 75 TwinDos bottles over the design life of the machine. The time cost of money to swap TwinDos bottles is $18.75. There is zero time spent filling the detergent drawer since TwinDos does this for you. That means the TwinDos system would save you about $1645 over it's design life. This assumes you value your time in this manner.
If you have to spend time refilling the factory bottles with your own detergent then you have to put five minutes into each bottle swap. That is how long it takes me to take out the bottle, refill it and reinsert. That means 6.25 hours spent refilling over the life of the machine for a time cost of money of $93.75. Even with manually refilling, the TwinDos system still saves you about $1570 over the next five years. Look at it another way: you have 104 more hours to go do something else other than pour detergent in a drawer. That is like having an extra 2.5 weeks of paid vacation over the next five years or 3.5 extra days of paid vacation per year.
Even if it saved you only half that amount, the TwinDos system still more than pays for itself in saved time. You also no longer have detergent spills or bottles sitting out in the laundry room. It stays cleaner.