My insurance covers glass with no limits as part of comprehensive coverage............so why would you want double coverage.
As for emissions coverage there are dozens and dozens of posts where even under the regular emissions warranty where the dealer has denied coverage. With MB customer service comments like the dealer makes the decisions.......which is just crazy and wrong..........but it's well documented.
Then there is the time period problem, five years from the date of purchase is not a five extension and might be no extension of the already emissions in some states as mentioned in post #70 ( if emissions are covered at all).
A lot of companies in Colorado do not offer a specific glass coverage due to the shear number of windshields getting replaced here (sand and pebbles used in winter). You'd have to file a standard claim, subject to standard deductibles. I'm sure some auto companies still do glass coverage as a standalone, but USAA doesn't (they did for us in the mid-west). The MB glass coverage has very low deductibles.
I have not seen a post where the extended warranty denied an emissions claim. Maybe I'm not looking that hard, though?
Even so, emissions failures rank low on my list of worries compared to a failed block, failed trans, etc. In my experience, factory-backed extended warranties often pay for themselves, at least when it comes to german cars with discerning owners. CPO'd cars are typically $5K+ more than non-CPO'd cars with the same mileage. Fidelity (underwriter for most Porsche and Audi aftermarket warranties) is usually in the $2,500 - $3,000 range for a 3/yr/36k mile powertrain warranty on a car fresh off the factory warranty (50k miles). Even a CPO'd Audi only gets you to 6yr/100k miles from the original sale date.
So, if the engine-only warranty on MB is 5yr/100K miles, but the driveline, trans, and everything else ends at 3yr/36k mile, then I fail to see how a $4k factory-backed warranty that is essentially a CPO taking the vehicle out to 7yr/175K mile is not a good deal.
If you're a DIY person, don't have a dealer nearby, or don't plan on coming close to meeting that mileage limit, then maybe it's not worth it to you. For me, we are buying the van from the same dealer that will service it, and they are selling us the extended warranty. They're also just down the road. I've worked on all my own cars for my entire life, so I'm looking forward to the convenience of MB picking up and dropping off our van for service, and all the other conveniences and perks of the warranty (like towing to a dealer if you break down). I'm not saying it's right for everyone. I'm just posting my rational and experiences.