The X3 was redesigned for 2018 – and it was a good redesign. The center became 3 inches wider and can now accommodate more car seats & boosters than before (where almost nothing fit in 2C). 2C also now has a flexible seat belt buckle.
There are 2 versions of the X3 – the X3 and the X30 M40. The back seats are identical, except that the M40 (a more expensive version of the X3) has a recline option for the back seats.
While 2C’s head restraint is not removable, there is room to pass a tether strap underneath it.
The X3 was redesigned for 2011. 2C became unusable for most car seats & boosters with this redesign because 2C’s buckle is now rigid (it had been flexible) and this made 2C even narrower than it had been before. 2C’s head restraint is now a distinct head restraint (earlier models it was a protruding part of 2C’s back rest) but it is not removable. This is mostly irrelevant since we haven’t been able to find any forward-facing car seat or booster that is narrow enough to fit in this 2C – the only thing that fits are some infant seat bases (like the Chicco Fit2) and some rear-facing convertibles (like a Clek Foonf).
The X3 was first introduced in 2004. 2D & 2P have rigid buckles while 2C’s is flexible. Due to the head restraint for 2C being fixed and protruding and non-removable, forward-facing car seats & high back boosters will not work in 2C. The only thing that fits in 2C are some infant seat bases (like the Chicco Fit2) and some rear-facing convertibles (like a Clek Foonf). 
