I have overheard BA gate staff telling passengers that their non-Yoyo pushchair was not allowed on, even though the passengers thought it would fit. YMMV.
We have been using a Cosatto Woosh, which doesn't fit in the overhead lockers but does fold up nice and small (and is therefore useful when travelling). We always gatecheck it, and we used to wait for it at the gate on arrival. Out of 8 or 10 flights, it ONCE was waiting for us when we disembarked. Other times we had to wait ages (while everyone else was getting in immigration queues), and several times it never turned up and we had to carry our daughter through the airport. It's amazing how often the orange tag "falls off" at LHR.
Anyway, what we now so is gatecheck it but don't have the orange tag - i.e. we get it at the carousel and use a sling to get the baby through the destination airport. Sometimes it goes go outsize baggage, sometimes it doesn't, but at least you know not to wait at the gate.
We have also been using a custom-made bag for it, to keep it clean and dry: https://www.cgrbikegear.co.uk/component/virtuemart/?page=shop.product_details&flypage=flypage.tpl&pro duct_id=220&category_id=7
The bag itself got damaged on our last flight into LHR but the pushchair survived. The Woosh is great - we also use it at home when we don't have space in the car for the "big" buggy.
Having said all of that, I have a friend who swears by the Yoyo, for travel and for day to day use. So there you go.