The weight rule
One natural lash carries one extension safely, and the extension should be no more than about twenty per cent longer and no heavier than the lash it sits on. That is the whole of lash safety in a sentence and everything else follows from it.
Which is why volume is not heavier than classic. A 0.07mm fan of four lashes weighs about the same as one 0.15mm classic extension, because four thin things weigh what one thick thing does. The fan looks like four times as much and weighs the same, and that is the entire reason volume exists.
Mega volume at 0.03mm goes further still: fourteen lashes in a fan, still within the weight budget. It is genuinely the lightest thing on this menu and it is also the one people assume must be the heaviest.
How many you have
Most people have between ninety and a hundred and fifty natural lashes per eye, and they are on a growth cycle, so at any moment about forty per cent are too short to work with. If your natural lash line is sparse, a classic set will look sparse: one lash on one lash cannot fill a gap that has nothing in it.
That is when volume is the answer, and it is a technical answer rather than an upsell. Iris will say so at the map.
Choosing, practically
Never had extensions: classic or hybrid. Shorter appointment, gentler learning curve, and you find out how your own lashes behave.
You want obvious: volume. Not mega, unless there is a photographer involved.
You want to stop wearing mascara: hybrid, at a modest length. This is what most people actually mean and it is the most-booked set here.