I have a spin bike at my house which gives me a similar workout to a trainer would. It sounds like you are more concerned about getting exercise and improving fitness in the evenings as apposed to needing to get out an enjoy being on your bike outside. I would say get a trainer for indoor training . I usually get a much more focused and intense workout on my spin bike doing intervals than I can in an hour on the road when I am stopping/starting for stop lights and other people etc.