Are either of the lighting detectors good enough tools to be IFR and avoid imbedded TS’s?
I'm mostly in the same camp as Ryan.
By themselves, no, unless you're flying IFR and are either on-top where you can see the cells or underneath and can see the bases. In the clag, though, I want something more.
Back when NEXRAD wasn't available and onboard radar was not a real option for small GA, the Stormscope/Strikefimder were the only weather avoidance options other than the MarkIII eyeball. When I first got my plane, all that I had available was a Stormscope in the place. We tended to fly to the limits of the tools, not trying to go anywhere/anytime.
With NEXRAD (I used XM/Baron weather services), we suddenly had all kinds of other tools. NEXRAD was fine for showing where the cells were a few minutes ago, and watching it for a couple of cycles you could get pretty good at estimating where they were moving or building next. With a little interpretation, one could add the display on the Stormscope (which was immediate display of strikes) to aid the tactical avoidance of cells an building cells. Under the right circumstances (knowledge gained from experience) I was OK with flying through the clag to get on top - I still wanted to see where the buildup S were to give them plenty of berth.
Traffic display added to that: now you could see what other folks were doing (including airliners that were low enough to display) and improve your interpretation skills. ATC could help, but their radar display was not as good as good NEXRAD. For example, coming out of ABQ one day I was headed for a hole east of town - ATC confirmed that other aircraft were going through there with a good ride, a couple that deviated from other routes (the deviation info being really great).
So I see them as tools with limitations, each adds something, but doesn't give the whole picture. Interpretation is required, and that requires experience. Just like any other tool, exceed its limits and you are asking for trouble. These days, I wouldn't fly hard IFR in the clag with just a Stormscope, nor with just a NEXRAD display. But taken together, I might (assuming recent experience and knowledge of the local weather patterns).