Speed is abrasive and while not terribly aggressive, it does remove clear coat with use. I`d restrict to using it at most once per year, or simply as needed. The more you use it the more material you remove.
Poxy is strictly a sealant and is non abrasive. No worries using is as often as you like.
Weekly seems a little excessive with either though. While poxy isn`t the most durable sealant out there, you should be able to get 1 to 2 months out of it before needing to reapply