I have the same question in regards to the Elite MPX. The use of gel is "suggested" but not necessary. Does anyone use it without gel?

The main reason ,speaking about the lasers ,is that if you fire the beam ,without gel and there are unshaven hair in contact with the cooling glass ,you will end up with a carbonized hair stacked on the the glass.effect :loss of energy and overheating of the carbonized pinpoint ex hair so burns occur.
So you have to replace the glass.
Bbl crystal is from saphire and hair do not stuck .gel according to my opinion is not necessary.is messy,optical coupling is not of clinical significance.

Gel, being mostly water, serves two additional purposes. First, it acts as a thermal coupler to help the chilled crystal effectively cool the skin. Heat travels much more easily through water than air, and the gel helps fill in any gaps between the skin and the crystal surface. Secondly, the gel serves as a heat sink after the pulse, helping to cool the skin by continuing to wick away heat even after the chilled crystal is removed. Because water has a much higher specific heat than air, skin covered with gel cools much more rapidly than without gel.

Both of these benefits make the treatment safer and more forgiving.

Clear gel does not filter much, if any, visible light - which is why they're clear. Colored gels filter a clinically insignificant amount when they're a thin layer. The BBL emits only visible light, with the too-high and too-low wavelengths being filtered out by a fixed short wavelength filter and interchangeable long wavelength cutoff filters. The gel doesn't affect the delivered wavelengths.