Yes, I have a Hagon on the Dommie and a Nitron on the M750.
I've had the Nitron for 7 or 8 yrs, the Hagon slightly longer.
I'm happy with the performance of both.
Don't read too much into that though .. I may not be the most competent judge of rear suspension performance and anyway, its not like I race around on the Dommie.
In terms of external build quality though, the Nitron is the clear winner.
I particularly like its square-form body thread for the preload adjuster ring, which also has tommy-bar holes rather than c-spanner castellations and this is a far better system in my view.
Both have held up reasonably well over time. The Nitron wins here but then the monster gets coddled in the winter while the Dommie braves the salt.
Is the bike a keeper ?
If so, I would go for the Nitron.
If not, the Hagon will do a fine job and save some cash.
Do you ever carry a pillion ?
My Nitron has a remote preload adjuster which enables simple adjustment between solo settings and something more suitable for carrying a pillion or heavy luggage.
I don't use it often but when I do its priceless.
And its handy for experimenting with minor adjustments to rear ride height/ steering angle, or perhaps sharpening up the steering for a trackday.
I mention all this because I got my remote adjuster at half price in a Christmas deal from HPS .. a deal which they often repeat and I believe its on offer this Christmas too.
...in fact I have the same system on the Dommie/Hagon as well, but had to pay full price.
It came in extremely handy when I had to fetch multiple bags of building sand from the local B&Q.
(I don't run a car anymore).
ps. I can't remember now but I would have thought that Hagon would be very much able to supply a spring tailored to your body weight.