Hi Nightryder, welcome to ECF
I started with an elusion, so I might add my 2c worth. I have the larger 1023, so I can't vouch for the performance or battery life of the new 1123, but I expect it's much of a muchness.
They say that each pre-filled catromizer will last 150-300 puffs. I would say that it's much closer to the 150 puff end of the spectrum. This means that at most you'll get about 15 analogs worth of vape out of each one, rather than a full packet as they claim. Since I only smoked 15-20 analogs a day this meant they lasted about a day for me, which was OK. If you smoked more this could be a point of annoyance.
You can fit spare cartos in the PCC it came with, so just make sure you're not caught short when you're out and about.
As everyone here's already said, you can tell when the carto is running low because the vapour production will decrease to almost nothing. At this point it pays to check that the battery hasn't gone flat. But if your battery is fine it'll be the juice running out. You'll find that if you keep going past this point you'll get a burnt taste. Best to avoid this, as it's a bit icky. Burnt filler also makes it hard to re-use the carto if you're filling them with your own juice in future.
The longevity of the pre-filled cartos seemed fairly consistent to me. I only had 1 dead one out of the 10 I ordered (seemed to have no juice at all). It does get expensive importing the pre-filled cartos from NZ, though. So I switched pretty quickly to filling the empty ones with my own juice. I seemed to be able to fit more juice in the cartos than they did, so they lasted longer per fill. I'd advise caution when doing this, though. The elusion has an automatic battery, so if you overfill you will have juice drip into the battery body causing epic hardware failure.
One other thing I will say: make sure you take long, slow draws. If you suck on it like a normal ciggie you won't get the proper flavour/vape. You'll also find that sometimes you get too much (even leading to juice in the mouth), or too little in any given draw. This may be a factor in the inconsistency you're getting. In which case, practice makes perfect
