Specflue are ( or were!!) a trade only supplier. Liner from them is high quality, either 316 ( 10yr warr) or 904( 25 yr warr), their warranty deal is unequalled anywhere.
Housecoal is NOT a fuel to be used in a stove, that why it says on the bags for use on an open appliance only or not for use in a stove. The reasons for this are twofold, A, it burns very dirtily and will clag up your glass, and B, if burning on a low oxygen setting such as overnight slumbering ( which is not recommended by any stove or flue manufacturer due to the amount of excess soot ( and tar with wood) deposited in the chimney and particulates sent into the atmosphere) then if you get up at say 2am and decide to put a bit more fuel in when you open the door you allow a massive amount of oxygen to enter the stove, an explosion could occur, called backdraft. Firemen here will be familiar with backdraft.
In most multifuel stoves you can burn wood, smokeless man made fuel and Anthracite ( natural smokeless coal). Air control settings are different fopr wood and smokeless, your dealer should advise.
Whoever is signing the job off as safe to use can be held legally liable if the liner fails and causes damage, death etc. For that reason most good quality installers will not work with customer supplied liner, I have seen web bought liner come unwound when being installed into a chimney before use. Like most things you get what you pay for I am afraid. If you go that route you would probably have to install it yourself ( to building regs) and get it signed off by a local building inspector.
If you use 316 grade liner and regularly burn smokeless fuel almost all of this fuel is imported, it has a very high Sulpher content, when it burns it will deposit acidic residues in the flue especially at low temperatures, these will kill 316 liner pretty fast. For any fuel burnt regularly other than wood use 904 liner. 316 will handle wood and occasional use with smokeless only.
A