We upgraded our car seat about a month ago. Brandon was just not happy in the infant seat any more and it was getting very difficult getting him in and out of the seat. Of course, I researched A LOT of different car seats for a while and finally settled on the Diono Radian RXT for my car. I ordered it through Amazon (where I seem to purchase everything nowadays) and with shipping it cost about $225ish (I can't remember the exact amount but it was around this price). One of the reasons I decided to go with this carseat over others were all of the features it had. Plus, it will convert down to just a booster seat so I knew I wouldn't have to buy another EVER!!! (That in itself pretty much sold this seat to me).
Out of the box, it was pretty much ready to go. All I had to do was unfold it, adjust the straps to fit Brandon and then put it in the car. My car has the LATCH system so installing was a breeze. I will say, this seat is pretty heavy but I don't mind because it's not like I am going to be lugging it around or anything.
The seat is pretty large height wise. I have it installed in the middle of the back seat because it will not fit behind the seats. This isn't really a problem because the width of the seat is a bit narrower than most convertible seats so it still leaves plenty of room on either side for someone to sit.
I will say that drives with Brandon have been so much better since using this new, bigger car seat. He has much more room and can now fall asleep in the car (something that rarely happened before). He doesn't fuss as much getting in and out and just seems much more comfortable.
Now, original plan was to purchase 2 of these seats so both myself and Nick could have a car seat in our vehicles without having to switch it out contantly. Well, Nick wasn't really a fan of having to thread the straps and we ended up finding the Evenflo Triumph at Target for $150 that doesn't have to be threaded and was still plenty big enough for Brandon to be comfortable. I don't think the Triumph would have fit as well in my car as it does in Nick's Durango. It is much wider and has a larger footprint than the Diono.
All in all, I am happy with both seats as we can now actually go places without Brandon freaking out after 5 minutes in the car because he is uncomfortable. I do think the infant seat was useful for the first couple of months but being that Brandon is on the HUGE size for his age he just outgrew it more quickly than most (he didn't outgrow it based on the height and weight limits on the seat but based on comfort and him being able to sit back completely in the seat).