Here's a question then John, what's the opinion of Heljan's steam / rod coupled models in HO world? I have never seen an appraisal of such.... believe me, if I get a chance to knock Heljan - I take it!
Edited to add what I forgot to put in when first posting.
In terms of RTR OO, I would assess Heljan as having been a positive contributor. Their centre motor twin bogie mechanism is a good solid performer, and when they get the body mouldings right* the models look very well, and coverage of both prototypes and 'pilot scheme failure' classes has been very welcome. But that's in large part because RTR OO started from a much lower standard than RTR HO stood at, back in 2001 when Heljan started in the UK market, and is still in catch up mode.
My opinion is definitely influenced by the fact that the four diesel classes that looked right and fitted my KX area late BR steam period modelling interest (TOPS 15, 16, 23, 26/0) have been trouble free, the class 128 has a useful mechanism for simple modification to power LNER full brakes, and despite the weird mechanism construction my two O2 2-8-0's cannot be faulted in operation. It's all been good for me... (I ducked out of buying a class 47, it was clearly the wrong shape, not even as good as Lima's bodyshell - which model I didn't buy either because neither the traction tyre nor the cheapo ringpiece power bogie are welcome on any layout I build..)
* I have speculated elsewhere in the past from what could then be observed on their UK diesel models, there was a near 50:50 split between well captured body shapes and 'sadly a blooper'. Could it be that there were two designers or design teams in Heljan, one very capable, the other not so much. I was told with great sternness: final warning, one more comment like that and you will be banned. Which suggests to me that I was probably right...