Teak is a naturally very durable timber and will survive for years without any treatment but teak oil doesn't do much other than make it look darker. Whatever you do don't use a sealer or a varnish, if you wanted to seal the timber then Sikkens make a range of finishes for this and I would use one of those. Otherwise Osmo UV protection oil is a good choice as it doesn't form a surface film in the same way as varnish so is much easier to maintain in the future as it will need little sanding down.

I would check that they have used teak, not many manufactures use teak these days and you need to make sure that they haven't used a less durable timber such as sapele. If they have then I would definitely use Sikkens Cetol filter 7 as a basecoat and Cetol HLS as a topcoat to the colour of your choice bearing in mind the darker the finish the more durable it is.