Multiple designs, multiple battery size options, button placements, regulated or non, different 510 sizes for multiple size atomizers/tanks, tank and atomizer options and then hundreds of different stem/drip tip options.
Not to mention the materials they are constructed of: metal, bone, wood, clay, stone...
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No personal experience, they seem to be resellers of Chinese made e pipes. . They appear to be "entry level" e pipes. The prices are semi-reasonable but with limitations within the lines; tank and atomizers options, colors, styles...
HTH
I