On the assumption that you've got a Hub 3, if you mean the VM wifi boosters, they're not offered free any more, and you'd have to rent them at £3 a month, which is poor value, so don't do that. In a year you'd have paid almost the amount to buy your own outright, and their has been criticism from some users of the quality of the VM boosters, but I've never used them so can't say.
You say you don't think you should pay for it, and I'm not here to say whether you should or should not, all I can say is that the VM hubs are built down to a low price, and have very modest wifi capabilities. In an easy wireless environment they can be entirely adequate. Demand more of them, or have a house with challenging wifi conditions (eg steel beam construction, solid brick internal walls, three or more floors or other issues) and they struggle. If you want to go down this route then consider spending £50 on the Tenda Nova PH5 AV1000.
Even if buying your own, a powerline booster will only help if you can meet the setup requirements. There's two units, both must be plugged directly into a wall socket (not an extension lead or multiplug), the first unit then needs a network cable to the Hub. And both wall sockets must be on the same electrical circuit. If they are on different circuits performance is usually impaired, or they may not work at all. So not that convenient a solution unless you can tick those boxes.
On the assumption that you don't want to run ethernet cables around the house, and you want a fit and forget wifi setup that's a big step up from a powerline booster, you should consider a mesh wifi system. I use and would recommend the TP-Link Deco M4, there's plenty of other options if you prefer. Avoid cheaper systems without gigabit ethernet ports. That'll set you back around a hundred quid, but its a one off expense and will work with all future ISPs if you leave VM. The Deco M4 is simple to setup and uses a single network name for 2.4 and 5 GHz, but manages this very well, unlike the Hub 3.
So, I think those are your options - or just putting up with the poor wifi of the Hub 3.
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