I haven't heard the Line 6 speaker, but have worked with several of 15/3-way speakers (Community XLT-46, Mackie's powered 3-way and ISP's powered 3-way). I haven't worked with a dual-10 PA speaker. My preference leans toward 12/2 designs (I own EV Sx200, Sx500, and RCF ART322) and most of the amps in my racks are QSC. I have used QSC K10 (main) and K8 (monitor wedges) at an installation I work twice a year. That said...
The Line 6 is 1/3-more weight (58 lb vs. 41 lb) and $350 more costly. It would be a bit more difficult to pole-mount (I use Applied Electronics 11' crank stands for better dispersion in large rooms or outdoors). It is rated at 132dB max spl, and has a 100x50 dispersion. The K12 is good for 130 dB and has a 75x75 dispersion.
The K10s I've worked with are flown in a small auditorium, and have a nice, even pattern. My RCFs are 90x60 and have a bit more "reach" (I've used them in the same room). Both sounded good once a bit of tuning for room resonances was done.
My suggestion would be to try a demo of both speakers, side-by-side, in as large a space as you can arrange. A/B same source, listen to the FR, walk the edges of the patterns, and make your choice. On paper, the Line 6 would go a half-octave deeper (not sure that's helpful until bass/kick/synth sounds are part of the mix... and a pair of powered subs would be good in that scenario) and the K12 might have a bit smoother mid/upper-mid "vocal" sound, as the Line 6 looks to do some DSP tricks with the second 10' driver in that region. But that's a guess...
In my search about six years ago for a "bang-for-the-buck" and single-man-portable solution, I chose RCF ART322As. I've yet to regret that decision. I own six of them, which makes for a great 2-main (over Mackie 1801 subs), 4-wedge system, or a 4-speaker meeting/banquet room setup (up to 800 seats), with a couple of on-site spares. The only speaker I've heard that would, in my situation, be a step up would be Meyer's UPQ-1P. But that's a whole 'nother kettle of fish... and a whole bunch more moolah.
Let us know what you learn.