[Advise needed] Shoes for gravel bike

Looking at the specs the Specialized are good all-rounder shoes.

Giro have a reputation for not being roomy, although there is a High Volume (HV) version of the Cylinder. If you've got wide feet or a high instep they might not suit you. Difficult to tell from the product photos but it looks like they've got less tread than the Speshs.

Anything that will take an SPD (not SPD-SL) cleat

I've got on well with Shimano MT-series shoes, also worth looking at their XC series which are a bit racier/lighter and can be made more off-road capable with optional toe spikes.

There's loads of choice out there though - have a look at Northwave, FiveTen,or Bont.

If you intend walking in them you don't want them to be too stiff - most of the performance brands will give you an idea of how stiff their shoes are. If you're going with a heavily treaded sole just remember that they won't necessarily work well with the flat side of those pedals because of the grip pins, just depends on where the grooves are.

I've got a pair of (last-season) MT5s - fine for walking in the woods, just about roadie enough to not look out of place on a road bike, very comfortable with adjustable speed laces

You can use any SPD cycling shoe or regualr street shoes with those pedals. The former allows for comfortbale walking off the bike as the cleat is recessed.