Mercedes pricing for the service packages is just outrageous, especially bearing in mind they'll be paying the dealer a pitiful rate for doing the work. There's also no incentive to take the package, possibly except if you live in the London area where the dealers keep servicing prices high.
Value wise, much will depend on your mileage and whether you are able to take time off work to take the car in for it's service. (Cheapest option is to take the car in and leave it for a day). I can't personally do this.
If, with a new car you are doing 13-15k a year then the service plans may suit you.
You don't have to take them out straight away - you have until the car is one year old. The plan must be sorted/signed up before that date arrives.
I recently (mid Oct) got info on one for my C220 as first service was due this month. They offered a plan for the three years I want main dealer servicing. Price is £972 inc VAT and can be paid monthly with 0% agreement.
Cost of a,b,a services for the three years is £835* On top of that you have brake fluid (app. £110) and possible additional costs on the B service (filters, possibly plugs etc) and at 37k miles auto box oil change at £240.
*Thats cheaper cost. Collect/service/return which is offered with the service plan is £925.
So, cheapest scenario for 3 years at dealers is £835 + £110 + £240 = £1,185.
This makes no allowance for filters or plugs etc. which may be required and gives a £213 saving.
Actual scenario for me is that I want the car collecting/servicing/returning from my workplace. This cost is £925 + £110 + £240 = £1,275.
So I pay £972 for three services that would cost £1,275+