No, it is not recommend and could be potentially dangerous to use the Gibbon Slacklines for high lining. The main reason is that it uses a ratchet to tighten the slackline and this piece is not rated for climbing or anything else that matter. A big problem of highlining is that the main line needs to be tensioned significantly higher due to the typically longer lines used and any resulting falls will place even more forces across it. Some hignliners use a triple redundancy system of 2 webbing pieces (often stronger polyesters or beefed up nylons) with a static rope or Amsteel Blue line inside each other for maximum strength and follow the climbing SERENE (Solid, Efficient, Redundant, Equalized, No Extension) acronym to ensure that the highline's anchor points are fully secured.
"Technically" you could use this to high line but it would require a secondary rated backup line in case of your main high line fails. In the end, it just not worth it.
There's plenty of resources online that you can find more information on highlining. Below is one such example.