And I'd still rather see a mortar halftrack than the US mortar. It also fits the theme better and is much more worth a doctrine spot than the US mortar. I'm just worried that the commander might be a bit on the lackluster side seeing as how it already has so many call-in units and one of them being the US mortar really doesn't help.
Yeah the Tac Support Regiment already has the dropped mortar but historically speaking I don't think the Brits actually used the variants of the US Halftrack, or hell even the M1 81mm mortar itself. The 4.2 inch mortar is a pretty interesting unit in itself as RoastinGhost proposed/designed it but then again it doesn't fit the theme of the commander since it's not lend-lease.
I think bundling would be the best option here, you'd have a Light Vehicle bundle with the M5 Stuart and one of the Halftracks and a "heavier" vehicle option where you'd get the M10 and a Sherman of some sort since the Brits did use quite a number of Sherman variants but I don't see much of a reason in an M4A4 for them since it'd basically fill the same role as the Cromwell but having an MG instead of a commander and some different abilities.
Similar to how the USF Mech Company was done but balance is a bit finicky and you don't wanna overload it with units/features/abilities obviously but it's quite the problem of trying to make it work as a commander that gives the Brits a more aggressive playstyle and yet still fits to the theme of a "lend-lease" commander while not feeling underwhelming in certain elements like it's call in units.
I think the problem lies in the fact that the Brits in general lack any sort of vanilla mobility so even the little which the American mortar, M3 and M10 provides for them seems both a lot but when compared to others seems quite not enough.
All in all in hindsight it's a commander designed to fill the holes in the British roster of units, unlike the USF for example which doesn't need indirect fire units that don't cost fuel, or a fast and reliable TD, or have problems fighting enemy when their own infantry isn't in cover. To the USF all of these and whatever their commanders provide are simply alternatives, not something that would entirely change how they would be able to play.
Really when you look at it the only thing that the Brits have over the USF is their tanks like the Churchill that can take a punch compared to anything American, even the Pershing, of which you can only field one.