it is a question of u want convenient or want result?

want result - directional type 3g antenna (whether yagi shape, panel shape...  panel will be small and lighweight, booksize)

want convenient - just bring your 3g usb modem around, it is built in with omni antenna 2 dbi sth, there is no need add in external antenna if you always on the move.

(omni antenna coverage area is a donut shape, NOT a ball shape. lower omni dbi = thicker but short donut; higher omni dbi = flatten but longer donut.

3g signal source come from base station, base station sit at high rise building to broadcast downwards, not same floor with u. using higher dbi of omni antenna (with flatten donut coverage shape) may return the opposite result of what u have expected (especially if u at ground area). this is not same case with wifi scenario where the router always sit at same floor or 1 or 2 floor gap. that's y till today i don't bring in any omni 3g antenna bcoz of no guaranteed gain on every situation)

higher dbi by 3G yagi = longer size, this for sure.

that's y u have the option to choose panel type directional antenna (most like a size of book, around 600g sth)