Depth of discharge will be controlled by the devices CUT OFF VOLTAGE, most ECig mods, have a cutoff of 3.0-3.2 volts. I believe the TM cuts off at 3.0 volts, same as my IQ2. Pulling them out, or recharging before empty, will just decrease your vape time, to baby a battery. Personally, I want the longest runtime I can get, which means at least a 15 amp., 3000mAh battery, like the VTC6. Yesterday, I ordered 8 of them at $6/each. Also using a quality charger will be best for long term battery health.
As far as charging, while it’s true you can get a bit more life out of a cell by under charging to 4.1 volts, instead of the default voltage of 4.2, you would need a “good” charger, like the SkyRC MC3000, or similar that allows you to set charging parameters, or try to manually do it, not very convenient. Anyways, the general consensus is, since 18650 batteries are much cheaper and more available now, buy new ones when the performance drops, rather the chasing after a few extra cycles. Not sure where the “3-4 times longer life” comes from?
*And as we discussed just recently here, charge em up when you get them, because they are often shipped with the 3.8 volt “storage charge”, and you want to start vaping with them full, for fun, a lithium battery won’t be damaged or lose capacity if you don’t charge them first, they will just stop delivering power when the device reaches its cutoff voltage.