This is difting away from topic a bit but...
If you are handy with a spanner, etc. give it a go yourself. It's easier than say changing a wheel bearing
The instructions that come with the unit are brilliant:
Step by step guide with tick boxes so you don't lose your place, clear photos, important measurements, list of tools ...it's all there.
Back on topic, my vote is for air lockers. True they are expensive, then there's the old adage ...you get what you pay for