For me, a huge consideration is to deliver a warrantable product. For all t hat you mentioned, I stay away from the prepainted Hardie. I never put any up for >>exactly<< the reasons you state. Shingles are colored by batch, and one manufacturing run doesn't match another exactly. Wallpaper, the sa me. Batch runs of tile, paneling, brick, and on and on don't match one ano ther. So how could batches of Hardie? Since it is expensive, you only ord er what you need, and if you need to go back for more, your prefinished pie ces don't match.
Hardie flip/flopped on caulking joints on the prefinished product since the ir own caulk didn't match, so when the launched the product we were to caul k; several years later, no caulking on the prefinished stuff as per their i nstruction. So what gives? Same product, one is painted, one is not. Worse ,the ambiguity of their instructions make sure they warn the potential inst aller to be aware of the fact that on long runs there is enough thermal mov ement that the joints SHOULD be caulked.
So what is the message? On houses with long runs, don't use the prefinishe d?
But it gets worse. Since no one reads the instructions, they don't flash E ACH butt joint as required. Every one should be flashed. I am the only in staller I have ever seen that does it though, even the largest "certified" installer here locally does not. So if you don't flash the butt joints and don't caulk them, you will get water behind your siding.
Prefinished siding from Hardie doesn't match their own recommendation of fi nish thickness on the siding. Somewhere in their literature they require a minimum protective finish (latex paint) of 1.5mm. They may have changed th at by now. However, a the time I measured the demo product with my microme ter the factory finish was less than half that. The Hardie rep assured me that it was fine since it was applied in perfect factory conditions to thei r specs and under their supervision. Bullshit. Too thin is too thin. The prefinished product is soft, scuffs and damages so easily that simply move ment of the material can cause scuffs, and scratches that require repair. And no paint, regardless of the accuracy of the original quality of color m atch will wear to the same color as a dissimilar product used by the factor y.
That being said, Hardie has its place for me. I have used a lot of it and had great results. As Leon said, primed is the ONLY way to go. Since it i s almost never stored correctly, primer provides a little protection agains t water and humidity absorption. I only buy from one local lumber yard tha t sells a ton of the stuff as it always fresh from the factory.
The pre-primed material holds paint very well, and one of the advantages of the preprimed is that you only need to put on a couple of coats and you ar e done. Properly painted, it looks great for years and years. Many compan ies like Sherwin Williams have modified some of their formulations to accom modate cement board products.
If I didn't have an airless, I would still wouldn't use prefinished. But a s I do with a lot of installs, I would prefinish myself. It is easy enough to lay out Hardie across sawhorses and roll it out. It takes no time at a ll to roll a couple of coats and they are are ready for use later in the da y or at least by the next day. I can put a helper on a 6 inch roller with a five of paint and he is a busy boy, but a helper can now pre-finish your siding on the ground. Scuffs and touch ups will match as you are using the exact finish you applied, and your nailer/installer can do his own touch u p before moving a ladder if it is more convenient.
Just thought I would put all that out there in case someone is thinking of Hardie or any other kind of cement board installation. It lasts well when p ut up correctly, but you must follow the instructions perfectly.