Considering wax oil treatment,

Has anyone gone down the wax oil treatment road. Mine can be done for around £500 locally. Is it worth doing?

Most people who intend keeping their Jimny go for underbody treatment. In addition to Waxoyl there is also Dinitrol and Lanoguard.

I am considering Dinitrol for my Jimny, but make sure the place doing the job properly cleans and dries the underneath first, this is usually a 2 day job.

Robin

I believe Lanogaurd and Waxoyl need redoing every 12 to 24 months. Dinitrol is much harder wearing, is jetwash proof and only needs touching up if you manage to scrape some off, on rough ground.
When I had mine done in 2019, the garage offered a free anual inspection and touch up, if required 

I use waxoyl and am aware that it needs a top up every year on high abrasion surfaces like the leading edges of axles and in the wheel Wells but that's to be expected on a working vehicle. The rest is as good as when I applied it 3 years ago.

That depends on what sort of job they are going to do. To do it properly they will need to remove the wheels, arch liners, headlights, both bumpers and the exhaust backbox. £500 would be reasonable for an extensive job, but expensive for someone to quickly spray some waxoyl around the bits they can see.
I'd also recommend something better than waxoyl if you're not planning on topping it up every so often.

The Gen.4 has extensive underbody treatment and a 12 year anti-corrosive treatment. This needs a check every a2 months but my local main agent told me that Suzuki would accept the stamp of a reputable dealer if I didn't want to pay £40-50 at the Suzuki dealer.
Last year I started to paint the underbody with bitumastic paint but gave up half way along when I saw how thick the Suzuki protection was. I might finish it this year, primarily because there is a small amount of rust on the front axle. It's nothing to worry about, but I am a pedantic sod and I don't like the colour of rust.

Roger