How to efficiently access first element of all subarrays, i.e. [:,1] or explicitly [(:SWATI, :GWAT),:amt]

Hi,
I was wondering if there ist an efficient way to access the first element of all the subarrays in a ComponentVector of ComponentVectors?

using BenchmarkTools
using ComponentArrays #, LabelledArrays, RecursiveArrayTools


SWATI=ComponentArray(amt = [1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0], conc = [0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.10])
GWAT =ComponentArray(amt = 1.0, conc = 3.0)
u0 = ComponentArray(SWATI = SWATI, GWAT = GWAT)


@btime sum(reduce(vcat,[u0.SWATI.amt, u0.GWAT.amt])) # 5.175 μs (54 allocations: 1.98 KiB)
@btime sum(vcat(u0.SWATI.amt, u0.GWAT.amt))          # 3.912 μs (48 allocations: 1.72 KiB)

Or would this require defining the ComponentVector with permuted dimensions?
Further, I saw higher dimensional ComponentArrays mentioned in the README.md, but I have not seen any example how to generate them in the documentation. Could you provide an example of this, please?

Start with README.md and the ComponentArray construction and indexing examples shown in the issue. Reproduce the BenchmarkTools examples to determine the supported way to access the first elements and how higher-dimensional ComponentArrays are created. Done means adding a clear, runnable documentation example covering both questions.