I tested WAFs in the past, also ones from the big players and while they might block some cheesy stuff on the application layer, as long as they are not heavily tailored towards your application, they stop bein effective against most manual stuff.
Everything lower than application layer ist not a WAF btw, so I am not sure if you mean WAF or some Firewallish stuff.

Just stick to best practices and expose only what you really need to expose. When putting third parties in front of your stuff this als has data protection implications. If using it makes you feel better okay but it should not feel you more secure if you expose vulnerable stuff.