The SecureKid 400 has the sure latch that self tightens and I believe extra side impact protection.
Keep in mind though that there is a weight limit for using Latch. My car has a 40 lb limit, so for me the sure latch was pointless for my 43 lb kiddo. You should be able to find the vehicle weight limit for latch in your car's manual I believe.
Ugh! Thanks for that reminder, I completly forgot. Good grief, car seat saftey really should be a little more cut and dry, there are so many variables, no wonder people don't know, or can never remember the ins and outs of it all.