I'm flipping through the new TY British book and I'm struggling to see why anyone would bother taking mechanized arty
The static artillery is either just as good or better statwise than the mobile artillery, and like 2/3s-3/4s of the price. There are slight differences. AP and firepower (Abbotts are 4/4, static is 3/3), assault/counterattack (Towed arty is 1 point better than mechanized in each, though weirdly the static 105s have a better counterattack than the static 155s, while the SPGs both have the same value) and the max battery size for the towed arty is 6 instead of 8.
The fearless veteran 105 batteries with commando crews also look interesting. They're only an extra 2 points over the standard static 105s