Light gathering power goes as the collecting area. Area = πD2
The pupil of the eye has a diameter Dpupil = 0.5 cm = 5 mm.
The small reflector has an aperture Dreflector = 10 cm = 100 mm.
Area of telescope / Area of eye = (Dreflector/Dpupil)2 = (100 mm / 5 mm)2 = 400
The collecting power of a 10 cm (4") reflector is 400 times greater than that of your eye.