Acrylic extender

Thanks for all the replies; if I had a Homer Simpson 'doh' emoji I'd be using it now. How stupid am I not to research Tamiya's own products? I should have known of course. Still, always good to hear people's opinions.

On the subject of Humbrol acrylics, I've found a product called VMS SlowMo airbrush extender which is claimed to be Humbrol compatible. Has anyone used it?

Have yet to try the Tamiya product, but I have used Future (now sold as Pledge Multi Surface Floor Polish if I remember the name right). It really slows down the dry time and gives the paint a semigloss finish. Sometimes that's useful.

There was another thread about this where someone was using a Grumbacher acrylic retarder to help with brush painting, maybe worth looking into if the Tamiya isn't available.

I have used Tamiya’s acrylic retarder for brush painting.  It has done wonders for brushing it - no clumping, streaking, just smooth with great leveling.  I have a Fairy Swordfish awaiting paint so I might forgo the airbrush on this and go with the brush and Tamiya acrylic to see just how good I can get it going “old school”.