Powdercoating pre-treatment chemicals advice wanted

[billjam]

There has to be a few commercial powdercoaters out there with experience in the chemicals we use for pre-treatment of aluminium.
I have just finished building new chemical treatment baths for our aluminium powdercoating line and I have the opportunity to choose different chemicals for etching and chromating/conversion.
Apparently, similar chemicals are also used in the anodizing industry.

Historically, we have always used Chemetall Metalletch 291L (= hydrofluoric acid) for etching and Chemetall Chromicoat for chromating and are happy with their perfomance. The down side of Chromicoat is that a by-product is hexavalent chrome (chrome 6).

The local Australian agent for SurTec (of Germany) is offering two alternatives to Chromicoat, one is based on trivalent chrome (chrome 3) and one is chrome free.

I've read enough product data sheets to be aware of how each chemical works and what the maintenance requirements are, but at the end of the day, what I'd really like to know is how each of these chemicals perform and what they are like to work with long term.
We will be stuck with whichever combination of chemicals we choose now for quite a few years, so before I leap into the unknown based on the recommendations of a salesman, I would appreciate any feedback from anyone using these chemicals:
SurTec 609 - chrome 3 conversion coating
SurTec 640 - chrome free conversion coating

Threads without pictures are boring, so here's some of our new tanks under construction and undergoing GRP lining in my work shop.