While I really like my Phil Ted's E3 stroller, it would not be as great (or useful) without the doubles kit. This extra seat usually attaches below the main part of the E3 stroller, but it can also be attached above the main stroller as well, if you are using the main stroller with an infant and have to have the main seat fully reclined (if you've seen pics of the E3, you'll probably understand what I'm saying).
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br /One complaint that some may think would be common would be that the kid who has to ride "underneath" gets skimped on space or a view. This couldn't be further from the truth. My 2.5 year old son LOVES riding in it. He'll choose to ride under rather than over if I even give him the choice.
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br /Highly recommended!

I can't say enough good things about the e3 with the second seat. My kids both love the stroller and we spend our lives in it. It is especially good for us because we live in a European city center, so I'm often in places that could be awkward with a large stroller. The e3 is barely bigger than a standard stroller. The kids both want to ride in the back seat, (older child should always ride in the front, though) and my younger child often sleeps in the back seat.
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br /The only real disadvantages are the lack of recline and small storage area. Of course, there have to be some trade-offs in order to get an extremely compact double stroller. As others have remarked, the back seat (double seat in toddler position) does allow a child to reach the wheels if they really try. This has not been a problem for us yet, but it is something to be aware of.
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br /Having this stroller is like having an expensive sports car -- we get stares and comments and questions everywhere we go! Phil and Teds in their wisdom included the web site address on the stroller, so it's always available for interested parties to copy down. I think we've already sold several strollers for them!
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br /One downside: the stroller's pretty heavy, so I sometimes have trouble getting on and off public transport.

I have the sport double stroller and can report that it may just be the best piece of baby gear I have ever seen, used or owned. A must have if you have 2 little ones. It's smaller and lighter than my single Graco stroller and it maneuvers like a dream -- with one hand! Gets into tight spaces and you can back out easily if you get stuck anywhere. Storage space can be a drawback, but you have to give up something to get something this compact and well-designed. Phil and Teds does sell accessories that can expand the storage space. Best double stroller on the market and I did my research. A bit pricey but worth every penny! Really!