Roofer has fitted external AAV in place of open vent

I have recently had my roof replaced. Our external soil pipe previously routed straight upwards through the soffit and the tile. The soil pipe has now been cut and terminates just below the soffit capped with what appears to my untrained eye to be an AAV. I can only assume this was to save the time and expense of re-flashing around the existing pipework. The end of the pipe is now close to both a bedroom and bathroom window.

Based on information I can find, this does not appear satisfactory as there is now no vent on the soil pipe. It is also in close proximity to a window. Whilst it does not appear to be causing problems currently, I would rather remedy it now if it is likely to cause problems in the future. Rather than get the roofer back as I have doubts about his competency, I plan to simply extend the soil pipe above the roofline and fit with a vent terminal, using a dog leg to get around the soffit and guttering. Would this be satisfactory?

The stack vent isn't specifically to allow the drain's air to vent out, rather allow air to vent in when the branches discharge into the stack avoiding the traps from being pulled.

Though, yes, it sounds as if they have done it to avoid having to route through new soffit and lead slate it but they have taken precautions by fitting an AAV which allows air in to vent the stack during discharge but stopping the drain air to escape. How close is it to a window?

Good practice dictated that they told you what they were fitting and that it would need periodically checked.

AAV's aren't recommended for external use, however floplast now make and market one.
Make sure you have the right one if you intend to leave it, that said it'll be bakeries anyway after one hood hard frosty winter.