He can bind right? The Lyn Fury is always a good choice. It has enough weight and a siliconable dual o-ring response. The Kickside is also known to deliver failry good 5a play. Some people prefer double silicone so they buy two of them and have a lefover dual starburst Kickside. And the FH0 is also a good choice. Some dif-pads or a silicone recess will make a good FH0. The Takeshi modded ones are a possibility as well.
Another possibility that hasn’t been named yet is the Phantom by Shinwoo. It is economic and plays fairly good. I happen to know a certain someone who’s really into Shinwoo yoyos. If you want any info, it is better to contact him than me.
Addment: Most plastics with a litlle weight to them will work for 5a, you don’t need a “special” 5a yoyo.