Is there anything better than just normal teak oil to use on outdoor teak garden chairs and tables that will last longer? Every year I have to sand everything down and re-apply the oil but it only ever looks good for a month or so.
Better things than teak oil available, look at Barrettine Garden Furniture oil, done the hardwood slats on the table & benches, great finish lasting well,I applied two,maybe three coats. https://www.wood-finishes-direct.com/product/barrettine-garden-furniture-oil And Astra has beat me in mentioning Sadolin Classic as well. https://www.wood-finishes-direct.com/product/sadolin-classic-wood-protection
There is a body of opinion that teak garden furniture doesn't need any aftercare other than a wipe down, and the silvery grey colour you get with new teak furniture after a winter outside is a desirable patina. I have a couple of teak Lutyens benches and don't do anything with them. As I remember they went that silvery grey colour pretty quick, I prefer it. As with any aesthetic it is of course subjective.
As Muzungo says, a lot of boat owners with teck decks and rubbing strakes would be horrified at the thought of oil or varnish, maybe just an application of teak cleaner every few years and a scrub with soapy water, and keep the grey colour.
Garden furniture oil - it is based on teak oil but often with UV protectors added. You need something which is absorbed and not just a surface coat.
Is there any reason why you should not use the Teak Wonder products? I know that most of the sailors will use them on their boats but I see no harm in using them on garden furniture no? My quick search on google revealed: https://www.foxschandlery.com/teak-wonder