My main transceiver for the past 5 years has been a Flex 6300. Before that it was a K3. Throughout the whole time, I've been a daily reader of each company's online mailing list and it's hard not to weigh the pros and cons of these American makers of first-rate gear, each still with very different philosophies despite new similarity in the equipment they produce.
I've only needed tech support once and it was made available to me immediately. The technician TeamView'ed into my PC, found the set-up problem and fixed it while I was on the phone with him. It took less than 10 minutes, was handled promptly and I've never had any other issues with my Flex, its software or the many 3rd party programs that work in conjunction with it. Despite Windows and despite what some naysayers spew, my Flex has been a solid performer - and I say that primarily as a CW DXer who dabbles in FT8.
Also, Flex is unique in offering a trade-in program for the purchase of one of their rigs. This program accepts just about any modern radio for trade-in credit - it need not be a Flex product. For a while, I considered trading in my 6300 for a 6400 and was offered what I consider a very fair amount for my 6300.In the end, I declined the offer and updated my 6300 to the new V3.0 version of SmartSDR and have no regrets.
Flex's SmartSDR has been around long enough to have spawned a collection of 3rd party programs that "enhance the operating experience". DX spots via the DX Cluster appear on my pan display. Clicking a callsign puts my Flex on the station's frequency. Or I can accomplish the same thing by running CW Skimmer. Either of these activities benefit greatly from having as large a monitor as possible - I use a 32" HDTV. I'm not sure when these enhancements would would be possible with an Elecraft K4 or if it will support point-and-click QSY with a mouse.
However (there's always a "however"):
Flex has a very limited product line (though less so now with the knobbed -M models). Some might see this as an asset - as in "they are specialists". Generational software updates cost money; incremental ones are free. The major updates are significant in what they offer and almost represent a "new radio". In going from V1 directly to V3, I now have more functionality than I'll ever use...but the noise mitigation controls in OpenHPSDR_mrx (available for free) are more effective with my little Anan-10e than those in SmartSDR for my Flex.
On to Elecraft - in their favor:
Everywhere that Flex is weak, Elecraft is strong. They have a diverse product line from QRP to QRO. Modular kits to already-built. Test equipment and antenna tuners. An online presence from the company owners. These are all major strengths that do two things: build confidence in potential customers and bring new hams into the Elecraft fold. Can't afford a K3s yet because you're just starting a family and trying to buy a home? Here's a less expensive model - welcome to Elecraft. Later, the home's almost paid for, the career is ramping up and the K4 becomes easily affordable.
A lot - everything - remains to be seen in how Elecraft will involve itself in the new (to them) world of direct-sampling SDR. No doubt their innovation will continue and, if they're astute observers of who's doing what, where, they'll look at SDRPlay as an example of how ideas can be implemented that will appeal to a wider variety of potential users while not sacrificing core performance factors (I'm referring to scanning and diversity receive functionality recently written into the software that supports these receivers).