For anyone who's interested, I've bought Rubicon's stowage set, M5A1/M8, M5A1/Recce and Opel Blitz (I plan to pick up the Crusader and M3 later).
Were they worth the wait? Most definitely! Rubicon have brought a new level of finesse and accuracy to these kits. A few observations on the kits (without having attempted any assembly):
The M5A1/Recce is lovely - it's quite a small vehicle, but the detail is well defined but not overscale. It includes optional additional features such as the rear stowage box and even a spare wheel (hooray!). The tracks and running gear are especially nice (the roadwheels are for the earlier M5 type, but it doesn't matter). I'm particularly excited about the Recce version, which provides a lot of scope for customising. I'm still not sure why the kit includes 3 .50 cals, but they seem to be slightly better than previous attempts at this weapon, so you'll have enough to replace the .50 cals on your earlier kits. The .30 cals are very nicely done, incidentally. Overall, Rubicon have managed to produce a kit which is detailed enough to please the modellers, but which will still be relatively easy and quick to assemble.
I haven't opened the M5A1/M8 yet, but I'm sure it will be equally good.
The Opel Blitz (which I suspect will be the most popular of these releases) looks excellent as well. The one piece cab is particularly impressive, and slips onto the lower cab body perfectly. The rest of the kit looks as though it will almost assemble itself. The detail is a bit chunkier than on previous kits, so for instance the tools are thicker. I think this is a positive development, and reflects the fact that most of these kits will be bought by wargamers. The crew figures are a bit rudimentary, but I'm glad they've been included, as modifying figures to sit in vehicles is very time-consuming. You can always replace the heads with heads from whichever figures you're using. One small point that I particularly liked is that the jerrycans which are included are the same as the jerrycans in the accessory set.
The accessory set is also going to be extremely useful. It has a good range of stuff, most of which will quickly find its way onto your models - especially the jerrycans, spare wheels and tracks, and the ammo boxes. I may be wrong, but I think a couple of the wooden crates look as though they are based on Soviet ammo crates (they're pretty generic anyway); if that's true, it's a nice bonus for detailing T-34s. The soft stowage is basically the same as Tamiya's 1/48 scale set, but scaled down to 1/56 scale. If you buy a few of these sets, you'll have enough crates etc for some very cool scenery pieces or objective markers. One point to note is that Rubicon's plastic doesn't stick to Warlord's (in my experience anyway), so if you're adding any of these pieces to Warlord models you'll need to use some kind of superglue.
The quality of these kits suggests that the next releases (such as the M10/M36 and M8) will be even better. In the meantime, I'm off to build the Opel...
