Darren asked that I put some text in here on the seat--so if you don't want to go through all the pictures this might be a little easier just to take a quick look over the pros and cons.
Britax Baby Safe 4-22lbs up to 30" (PLUS, per manual)
MSRP currently: $300
Pros:
Deep seat shell, tall seatback, easy to use puzzle buckle, footprop, rebound bar, obvious beltpath, light.
Cons:
Lack of a suitable stroller, confusing instructions when using seatbelt, poor fabric colour choice, footprop doesn't function smoothly.
First impressions after use of the seat:
If just the base is installed, it actually rattles around a little bit while moving. It's EXTREMELY heavy, so fortunately you don't have to take that part in and out of the car. The seat itself is really light. One observation I didn't make in the linked review (above) is that the harness doesn't really seem to be an easily gliding one-pull like the Roundabout. You seem to have to pull it twice to get it fully tight, although at the same time it doesn't rachet back like the Marathon and Wizard adjusters. Another observation I didn't make in the original review but will make now is that my son is about .5-1cm above the top harness slots. I haven't taken a tape measure to the seat yet but he's currently about .5 cm below the second slots on the Roundabout. I can't stress enough just how tall this seat shell is.
If you're spending $300 on a seat, you want it to last $300 worth. I really honestly believe this seat will do that, especially if you have taller/lighter kids. Considering the Companion is 2/3 the price, what do you get for that extra $100? The footprop--which is amazingly stable and really stops the seat from rotating back, and the ease of use of the rigid LATCH connectors. The rebound bar on the Baby Safe doesn't seem to catch as early on as it does with the Companion (there's a lot more movement) but I'm sure it does the job.
The stroller issue...I've been doing a little bit of research and there IS a stroller in the UK for the Cosy Tot, so I'm not sure what's going to happen here since Britax *just* released three strollers into the US market, two of which are Companion compatible (but not Baby Safe compatible).. I have yet to check to see if the Baby Safe can click into the Maclaren Global (the Companion doesn't, it sits there but doesn't lock) but I know for a fact that Kolcraft has recently updated their advertising blurb on their universal to include the Baby Safe.
If anyone has any questions, feel free to post. It's tough to give the seat a real workout since I have a 2 year old and our baby isn't expected for another 6 or 7 weeks. You never really learn what's going to annoy you with a seat until you have to get a child in and out of it a few times a day.