Sorry to be a bit late piping up here. I was hoping someone else might respond...
I have used the Alva. In fact, I should disclose that I've been an unofficial 'beta tester' and I know the designer.
I previously brewed using gas heating. Separate picnic cooler mash tun and all that. I've now moved to a 35L electric brew kettle, brew-in-a-bag (BIAB), and with the Alva to control temperature and pumping.
This new setup is much quicker (4-5 hours per batch) and makes brewing more reproducible. With my previous system, I'd have to make half a dozen batches of a particular recipe before I'd be reasonably sure of getting the same beer. With the precise mash temperature control that the Alva brings, I'm reasonably confident of getting the same beer at the second batch. If that's important to you, then I'd definitely say the Alva is worth considering. I've become a fan of recirculating BIAB, and most likely will never go back to a separate mash tun.
If you like to work with stepped mashes and the like, the Alva is perhaps even more useful. Myself, I generally use only a single mash temperature -- so this isn't so important. Still, it's nice to know the facility is there if I need it.
My kettle is 3kW and it has a typical "Burco" style thermostat -- a knob on the side. I once attempted to brew in it without the Alva, but found that the hysteresis in the thermostat was huge; my temperatures were fluctuating up and down by many degrees. The Alva deals nicely with this. The control algorithms are rather sophisticated, so it very cleanly ramps up to your set point temperature and then stays there exactly. So if you are already an electric brewer and looking for more precise control, the Alva is a good place to look.
Overall, I've come to enjoy the more relaxed brew days I get with the Alva doing all the measuring and watching! I have more time to concentrate on other aspects of the brewing process.
I'm aware that there are other similar controllers on the market, and also many DIY projects available on the Internet. Some are sophisticated, others more basic. Some are rough and ready, others polished. The Alva is well polished and pretty much plug-and-play, though as with most such systems you do need to have a suitable electric brew kettle, pump, etc.
If you have particular questions about whether the Alva is suitable for you or your brewing method, I would contact Tom at Alva Brewing. He's very forthcoming.
Steve