Just a quick review of the new Britax convertible accessories.  These accessories fit the following models:

Britax Roundabout 55, Britax Marathon 70, Britax Boulevard 70, Britax Boulevard 70 CS, Britax Advocate 70 CS and their Canadian counterparts.  They are NOT compatible with the previous “Classic” Britax convertibles (rated to 65 pounds in the USA).  Please note the photos below are with the Marathon 70.  Other models may vary slightly in terms of fit with the insert.

First, the Infant Positioning Insert, that retails for $14.99:

It is rated for use from 5-11 pounds.  It is easy to install.  You simply lift up the flaps on the cover and place it such that the bottom is under the existing comfort foam.  A notch fits nicely around the crotch strap.  The illustrations included in the instructions outline the procedure.  It takes all of a couple minutes.  Once installed, it moves a small baby upward and forward.  That helps boost them toward the lowest adjustment for the harness straps and takes out some of the space between the baby and the closest crotch strap setting.  Without the insert, most newborns will not fit into the Britax convertibles, because the manual says the baby’s shoulders must be as tall as the lowest setting for the harness straps.  Even with the insert, I would guess that most premature babies and many smaller newborns will not fit. 

For example, the Huggable Images 7-pound infant doll is very close, but does not quite fit according to the manual  (even though the actual fit is quite good).  I would guess that around 8 pounds or so, many babies will be able to fit very well.  Of course, babies vary a lot in torso height, so there could well be some that fit fine at 7 pounds, while others may not fit even at 9 pounds.  Overall, it is a very nice accessory if you plan to use the convertible from birth, rather than an infant carrier.  Here are a couple photos showing the fit on a Huggable Images newborn doll without the insert (left) and with the insert (right).  While you may only be able to use it for a few months, you can always give it to a friend or sell it on Carseat Swap when you are done!

Next, the Child Cup Holder, that also retails for $14.99

Not much to say about it.  It’s a cupholder.  The attachment easily hooks onto slots in the shell, under the cover.  Then you click the cupholder onto the attachment.   It swivels to keep things upright.  It is relatively deep, sturdy and has a narrower bottom section for slimmer profile cans and bottles.  It does take up room on the side of the seat, so it may interfere with an adjacent seat or door.  Fortunately, you can mount it on either side.  The only drawback I can see is that a child could push down with enough force on the bottle or can and un-click the cupholder from the attachment.