I have worked and driven Lotus 6s and 7 S1s to S4 cars and Caterhams when I was a college student in the late 80s early 90s at a place called New England Classics in Stratford CT. The best cars are the S3 and the Caterhams. None of these cars are known for their build quality, they are raw and rough, but that said, raw and rough gives you an experience that leaves you smiling. These cars handle very very well, and on the track there is not much that can keep up with them. Their biggest flaw is the lack of down force at high speeds. Those fenders shown want to lift the front end up, but that is really once you are over 100 or 110mph. I have driven these cars at Lime Rock in CT and you can go flat out every where except at the end of the straight into Big Bend (and I always chickened out on the down hill onto the straight and lifted at the top of the hill). Great track cars.
On the street they are lots of fun, you can reach out at a stop light and touch the road with your palm. We used to drive with dealer plates and no windshield on the Marrit Parkway with the center of the wheels of the cars we were passing at eye level.
I have never driven the later Caterhams with the Ford twin cams, they must be over the top quick.
This is the only car I would consider trading my 911 for (don't for get that my 911 is probably worth 10-12K). Just keep in mind the 911, is much more usable, and wife friendly and the most modified racing 911 is as comfortable as a stock Lotus 7. You need to get into these cars by stepping on the seat that is mounted to the 1/2 inch off of the floor, then lock your knees and slide your feet into the smallest foot wheel. If you have shoes bigger than a size 10 it is going to be really tight. You wear these cars more than you sit in them. Getting out is a matter of pulling yourself out and I heard someone say it's easier to fall on the ground than to get into these cars.
Once you are in the controls and steering are world class. The shifter is tight as a cats ass and every thing is instantaneous. You will scare the crap out of yourself and any passenger, and want to do it again and again. I would say the experience is like that of Jeremy Clarkson and the Ariel Atom.
YouTube - Top Gear - Ariel Atom - BBC