Clip on sunglasses should look fine over regular prescription glasses as long as the clip on lens is similar in shape and size and the clip on rims are similar in color to your regular glasses.
The primary advantage of clip on sunglasses is the inexpensive price compared to prescription sunglasses.
The major disadvantages of clip on sunglasses are scratching of the prescription lens and lack of side coverage to block out the sun.
Be sure sunglasses or clip on sunglasses have 100% UV protection.