We have an l25500, the newer 360 and a mimaki latex running cmykog+w and it is total garbage. I mean, total garbage. I've been running printers my whole life and we cannot get a quality print out of that mimaki for anything. The white ink is not opaque enough to flood with (mimaki confirmed this for us as well) so it's essentially useless. And it is SLOW..... vinyls run at at least 24 pass or higher for any kind of quality and other things run even higher. At this point we just keep it plugged in so the heads don't dry up. We are in the middle of buying a flatbed and we have required it to be taken as a trade in.
i love my hp's though! I just don't know what a white ink option would add that can't be accomplished in the finishing department (laminating clear to white vinyl etc). Maybe if it were opaque enough to flood as a blockout for two sided clings, but right now for two-sided window 'clings', we run 15oz two sided blockout or a thick poster stock as a cheaper option, and then put the gudy window adhesive on one side.