K.C.
Well first we have the trailer and the seat attached and also a tag-a-long. The tag-a-long is for a child at least 3 yrs.
I would purchase the trailer. The trailer is much more versatile then the seat connected to the bike. The trailer comes with a rain guard which I have used on more than one occasion. My trailer is for two children.
We are avid bikers and even though my youngest is now 4 yrs we still use the trailer ( or the tag-a-long)