I wouldn't bother with those convertible options. The light output on them even as full canisters doesn't make sense from an investment standpoint. Has been covered in other threads, but you can get about as much light out of the backup lights and by the time you make the investment to upgrade it to a canister light, your total investment is going to exceed that of a top end canister light and the backup light.
We'll use the UTD light for an example.
the Viz-2 35 costs $490. For that you get a single cree emitter with 3x 18650's. That single emitter can only output about 1000 lumens, and should be able to do so on high for about 2.5 hours with those batteries on high.
To convert to a canister you have to buy the new EO cap at $250, plus the battery with EO at $650, for a total cost of $1400.
They are lying on their burn times for the battery pack, completely impossible for it to get that much light output for 12 hours, that is a load of sh!t, 9 hours if they're lucky unless it doesn't actually stay a flat burn curve, in which case they're telling the truth about the hours, but lying about the output. Big Blue is known for this btw.
Conversely, you could get a UWLD-15 with the Tall canister which doubles your light output of the UTD, does it at the full light output for almost 7 hours *at the same output, it will go for about 10*, and is a much higher quality light, plus buying a pair of good backup lights for the same $1400
Dive Rite math works about the same for reference