You can do unvented cylinders off a stove without an H2 or buffer, so long as you make sure that you can maintain 3 tiers of safety control to prevent boiling.
The easiest way is to have a NC 2 port in the flow to the cylinder wired to the cylinder stat and cut-out stat to close when satisfied, along with the TPRV & PRV on the cylinder you will satisfy regs. A high limit stat on the flow to bring the heating / additional heat dumps will help matters.
You will need to consider how to dump the heat produced once the cylinder's closed, as the heat load on the system will dip, so you'll need to have a high limit stat on the solid fuel pipework to kick the heating into life when the flow temp gets to 75 - 80 from the stove. Heat leaks will need to be sized carefully too, in order to make sure that they can cope.
In some cases you can put additional gravity heat leaks in, where a large boiler stove on apumped system may go down in a power / pump failure. We have done a couple of these where we have put a heat dump array into the loft of a property with a N.O 2 port inline, which will spring open in the event of power failure or an overheat stat breaks.
The H2 panel is simply a few valves and stats wired in interlock, which doesn't give any more control than you can get on your own, it just makes it a lot easier to put it all together on a smallish system.
To be honest you can do a lot of things in real life that many people say are a no go such as linking a stove into a pressurised system or Linking into a Combi Boiler... It all just takes a bit of planning and the right kit
*Edit*
A buffer / accumulator tank is a great addition to a solid fuel system, so you can smooth out the heat delivered from the stove boiler
Thermal stores work brilliantly too with solid fuel, they make it much easier to live with as there is heat available when the stoves not roaring away.