I had a similar dilemma and here is what I ended up doing.
I have not personally moved off the Envisalink system but my DSC system is still actively working great and is still professionally monitored. I got the Envisalink purely to have the existing system 1) available to be controlled from the Eyes-On app and 2) being able to fully integrate it into SmartThings and SHM (My key requirement was I needed it to still be fully functional as a stand-alone monitored alarm system but also able to be fully integrated with SmartThings and most importantly be synchronized between the physical panel and SmartThings (e.g.: if I arm at the keypad, SmartThings also shows it as armed and vice-versa)
When I recently researched the Konnected options I noted two options: 1) the interface kit and 2) to conversion kit.
The interface kit appears like it tried to mirror what Envisalink does but accomplishes it basically by tapping existing alarm sensors, but doesn’t integrate with the existing panel, pull status etc. Envisalink wins that one hands down as with konnected interface you’ll basically have two separate and isolated ‘alarm systems’ sharing the same sensors. I’m failing to understand that use-case but I’m sure it’s out there.
The conversion kit on the other hand is compelling ‘IF’ you want to execute a wholesale replacement and decommission of your existing panel but need or want to reuse your existing hardwired sensors.
My problem is while I like SmartThings, I’m not fully prepared to trust my security system exclusively to SmartThings and it’s sensors and replace my UL keypads with an Android tablet or two - Too many failure points in my opinion where the DSC equipment is pretty darn hardy.
What I did was executed a nice upgrade and expansion: The first thing I did was add the Envisalink board which got me the internet control capability through Eyez-On and using Alarmserver I got SmartThings integration. The next thing I did was had my alarm company de-merge my zones. When my system was installed, the installer combined doors and windows and my motion sensors into a total of 6 zones. I had my alarm company add a zone expander board and split all the sensors into individual zones. That gave me 13 separate sensor zones (11 door/window and 2 motion) that I now have individual control over but also can be integrated and individually used/automated in SmartThings. The final upgrade was replacing my two old keypads with the DSC PTK5507 touchscreen keypads which by itself felt like moving from 1980 to 2010 (and as long as you are comfortable and careful, you can install/replace the existing keypad yourself).
Having the alarm company rewire the zones and the zone expander board cost me $165.00 and I scored the touchscreen keypads off eBay for about $100 each. Note that I did not have the installer code but since the alarm guy was redoing all the zones anyway, he reset the system and set it all back up clean - and gave me the installer code.
Benefits: I have a fully up-to-date alarm system that still uses wired zones (too many vulnerabilities with the current wireless stuff right now), with touch screen keypads, fully monitor-able by a UL listed monitoring facility, I have remote access to the system through both the Eyez-On app and SmartThings and full integration with SHM and all components are completely operable independently from each interface (physical keypad, Eyez-On app or SmartThings) but is fully and in real-time completely synced across all three. Plus I’m still only paying my standard monthly monitoring fee from the alarm company.