The pods are based on the Plume mesh wifi system. The hub runs Plume router emulation software, and the pods then synchronise to form a mesh wifi setup. It's not a bad system, and can even work quite well, but its unlikely to match even a modest dedicated mesh system for ultimate performance because the hub's hardware and spec was pretty feeble when it was launched back in 2016, and the compromises of both the Puma bug workaround, and then adding mesh emulation won't be helping. I'm not rubbishing VM's pods - for the technophobe, or those who are getting the pods free, there's much to like about them. But if you're prepared to read a manual, and don't get the pods free then I would suggest you put the money you'd otherwise have spent on pods towards a mesh system of your choosing. The TP-Link Deco S4 for £100 would be a good bet, but you can spend a whole lot more or choose other makes if you want.
The issue I'd expect they refer to is that the powerline boosters will be create a competing wireless signal. When used with the hub alone that's manageable, with the pods you've got one wifi signal from the hub, one from the pod (or each pod), and then a signal from a separate powerline booster. The hub and pods should work cooperatively, but the booster may not. Worst case is probably slow wireless speeds or dropouts. If you're lucky it should work, and you won't cause any damage by giving it a try.
Personally I don't like powerline networking, and whilst you might get away with hub + pod + booster, I'd see the optimal solution both economically and performance wise as a proper dedicated three unit mesh system with the hub in modem mode, with a second choice solution of using the hub and getting two pods if needed (though if paying for them that's pricey). A mid-price alternative is to use the hub as router, then just add a second mid-low cost router (eg TP-Link Archer C6) configured in access point mode, placed somewhere that optimises household coverage. You'd need an ethernet cable between the hub and access point, and these two would be broadcasting completely separate wifi signals, so if devices auto-switch from one to the other then that transition may not be smooth, whereas with a mesh system you shouldn't have that. You'd also have to take responsibility for manual wifi channel selection on hub and the router/access point to avoid the two reacting to each other and continually auto-switching channels.
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