There are numerous recumbent overview documents online. Here is just one. I live in a built up urban area I have seen one recumbent trike in 3 years. I've never seen a lowracer. Bicycle Man doesn't even sell lowracers anymore because they all get returned. Trikes and lowracers sit about the same distance off the ground. Very intimidating to ride in heavy traffic. A long wheelbase bent can approach the length of a DF tandem but will only carry one rider. They can only get so light unless made from carbon fiber ($$$). They remain popular because they can have much more predictable handling than the more sporting designs. With fairings and/or bodysocks they can be very fast. Highracers and lowracers are both considered SWB in layout and put the riders feet high and their heads low and this makes for a less intuitive handling paradigm. For those with the innate aptitude or the will to acquire it through practice they offer the reward of high performance and low weight. As always there are exceptions to every generalization.