You say you want to tone up but you dont want to add bulk? Well, generally the term 'toning' refers to adding muscle (bulking), then cutting (i.e. losing body fat to reveal the muscles). Since you dont gym as it is, Im going to assume youre lacking in the muscle department so adding a bit of bulk might be necessary

Personally, Im not a fan of these all-in-one home-gym equipment things. They usually tend to try do everything without getting much right.
Since you only want to do your lower body, here's what I would buy if I were in your situation:
1) Dumbells of various weights. With these I would do various lunges and dumbell squats.
2) A squat-rack with a barbell and some light weight-plates to start off with. With a barbell I would do squats (if you do them with correct form and sit back using your glutes properly during the squat your knees will be fine). Squats are renowned for being the best lower-body exercise as it works all the muscles.
I would also do Good-Mornings for the hamstrings and lower back.
I wouldnt work my lower body more than twice a week though. Anything more is overtraining.
Anyway, this is just what I would do. If like many people, you find the world of free weights a bit too daunting (I can never understand why), then I guess going with something like that Bowflex Sport is better than nothing. I just feel and know that free weights are superior to all types of machines.
Its a pity youre not interested in joining a gym cause they really are far superior to 99% of the home gyms out there. You wouldnt be limited for choice when it came to exercises. What exactly do you hate about them?
By the way, why dont you want to work the upper body at all?