I traded a CBR250 for my RT-S, don't make the mistake of believing that it is a "boring" 1/4 liter bike. I got it for a commuter bike, it would have worked for me when I was 40, but now that I'm an official senior citizen, and I did a +/- 100 mile ride on it, and reconsidered my decision. It is a very responsive, capable bike, the first time I took it up on the interstate I was well over 90 before I realized that a 1/4 liter was as capable as it is. I tip the scales at 235-240 depending on if it is before lunch or after, and I have been riding since 1956 so I'm not new to motorcycling, the CBR will do the job as well as many bikes larger in displacement. I'm not sure that it really would be a good bike to learn on, unless you are planning to stay in the sports bike arena. It will move as quickly as you want it to. It may not catch a BMW liter plus bike at or on the way up to the top end, but for under $4,000.00 and 65 MPG it is a great bike for the person that is still flexible, it really will surprise you.
If you get the opportunity, take a test ride. I've been on all kinds and sizes of motorcycles, scooters, (the first bike I owned was a Vespa motor scooter) I've ridden some of the fastest in class motorcycles, Honda's, Kawasaki's, big and small. Harley's, Indian's, and, no, the CBR was not the fastest, but it is probably one of the "sleeper" bikes.
I guess if you were looking for a good, challenging motorcycle and had a very low budget don't rule out the little CBR250.
Doc