hi,
anthracite is fine. it has the highest heat content when burnt compared to other coal, but requires a harder blast on the fire (or a touch of the loco steam blower, unless the loco is being worked hard) and can be difficult to light if you dont have a powerful electric blower fan and arent used to it. UK anthracite comes from western edge of the coal seams in south wales and is pretty consistent in its quality. some seams mined were of 'soft anthracite' more akin to welsh steam coal semi bitumous coal – you might get this depending how old the stock of coal is from which ever merchant you bought it.
anthracite wasnt used in fullsize due to it being the most expensive of coal and supply being insufficient for the railway's demands in years gone by.
welsh steam coal is only available these days from the Ffros y Fran opencast site near Merthyr Tydfil, and is of variable quality depending on what bit of the site is being worked on at any one time. proper welsh steam coal is relatively light in weight, and friable, easy broken by hand, irregular, and shiny. i suppose there is a bit of an art to firing with it and different techniques are required for different types of firebox.
ive got about 3/4 ton of anthracite beans at home but dont use it on my locos as i find the smell and smoke really chokes me up badly after a day's steam up. it gets at the back of your throat and most people find it quite unpleasant.
steam coal proper hasnt been mined on a large commercial basis in south wales since about 1991/2.
i would have said (from what my club obtained in the last few years) that the Signal Fuels stuff was soft anthracite (probably from Tower Colliery before it closed) rather than proper welsh steam coal. i wasnt that impressed with it!
occasionally one of the private drift mines gets to a seam of good welsh steam coal and word goes round and it quickly gets 'earmarked' and purchased by those clubs in the know. however this doesnt happen very often.
when you've used the proper stuff nothing else compares! luckily ive a shed full of the stuff!
cheers,
julian