Mark's nailed it pretty well and I'd echo the idea that Weatherlink Live (WLL) is best thought of as something a little different from a traditional Davis logger - WLL does offer many extra features but does not use the same API as older loggers and so is not compatible with the established software base
unless - like CumulusMX - the programs specifically offer WLL support. So, for example, even Davis's own
local Weatherlink (for Windows or Mac) can't talk to a WLL unit.
If I had to sum up WLL in one word it would probably be flexibility. So, WLL is completely independent of any existing console and can be placed in a quite different location (as long as it can still receive adequately from the sensor transmitters of course). Existing console(s) will continue to run quite happily in parallel with WLL and so any logger in an existing console can continue to pass data to any existing computer/program as normal, if that's what you want to do. Also worth underlining is that WLL can connect into your local network either via WiFi or cabled Ethernet.
As Mark says, perhaps the biggest plus is the ability to run literally any mix of transmitters on all 8 channels and so the inability of the old console/logger combo eg to run more than one anemometer, rain gauge etc etc is finally gone. And any supplementary temperature transmitters will be received in full 0.1°resolution (rather than the 1°F resolution that was previously the limit). Also, solar/UV sensors can be placed on a different transmitter from the ISS. Of course any software in use has to able to support this extra flexibility. I know that CMX already goes some way towards this eg allowing solar/UV on a different transmitter, but doesn't (as yet?) support for instance multiple anemometers. Probably the only software platform that supports pretty much all WLL functionality at present is the Davis weatherlink.com cloud platform, but doubtless others will join the party in the coming months/years.
For anyone not familiar with weatherlink.com this operates on a fremium model with a basic free plan and then a Pro plan with an annual subscription. Access to different features is then divided between the plans. But, in essence, access to all
current weather data is part of the free plan, as is access to the free smartphone app. For a lot of users, the free plan may be all they need, especially if users are also running CMX for local data storage/analysis etc. But weatherlink.com can do much more with the Pro plan and, for example, store, chart etc all of your
historic data as a backup for example. Weatherlink.com continues in active development and new features are in the roadmap for future addition.
I know that the subscription is divisive. But personally I'd argue that this fremium model is a reasonable compromise. Weatherlink.com now has around 50,000 users worldwide with a team of developers and support staff maintaining and extending it. It's not realistic in my book to expect that this considerable effort can be provided completely free of charge, but the free part of the plan does still offer substantial features and so that's perhaps a fair balance. But opinions will obviously vary.
There is a decent independent review of WLL on youTube at:
https://www.youtube.com/watch?v=1dmEn_mTTnY . I don't know who this is by - apparently UK-based, maybe even someone here? This is a worthwhile review to watch but, slightly frustratingly, doesn't really highlight the key benefit of the multi-transmitter capbaility and also focuses entirely on the smartphone app without also covering the better graphics and other features of the browser app. It also doesn't mention the option of connecting to local software like CMX. These omissions are perhaps a pointer to the fact that WLL is quite a capable device and not of all its features are obvious at first acquaintance.