DME is easy to remove from water in the case of spills simply by aeration. The atmospheric lifetime is about 5 days, meaning it has a negligible greenhouse gas potential. It is also non-toxic except in very large amounts. (It's physiological effects are rather like ethyl ether, it is something of an anesthetic.)
By contrast, OMEn ethers are difficult to remove from water, although, like DME, fairly miscible in it. The formation of acetals is reversible, meaning that they can be expected to release formaldehyde - which is toxic - and also methanol which is also toxic. Since these acetals are reversed by acid treatment, drinking water containing a OMEn fraction can result in the generation of formaldehyde and methanol in the stomach if ingested, not a good thing.
A large spill of OMEn might well be catastrophic and more difficult to clean up than an oil spill, inasmuch at least oil is immiscible and some can be removed with booms and the like.
I do have a difference of opinion with the "Green Car Congress" about what is and is not "green."
Again, in comparison to drawbacks, the need for slight pressurization is trivial compared to toxicology. We know from experience that any fluid fuel can and will leak into the environment, either in catastrophes like Exxon Valdez, or leakage.
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