Marco Polo uses pseudo Doppler direction finding by commutating an array of 4 antennas in the handheld locator at 1,375 rotations a second. This eliminates the need for you to determine a peak or null in the signal by sweeping a directional antenna back and forth because the Marco Polo locator is an automatic, not a manual, direction finder. Since pseudo Doppler is phase rather than amplitude based, there are no gain adjustments as you approach the target, it can literally operate 1-inch away from the transmitter just as it does 1-mile away.
All models of tag transceivers have the same 3-inch whip antenna but in the Ultralight model it is just a 22 ga. wire, whereas in the "Advanced" model, which has IP67 waterproofing, there is a rubber sheath over the antenna wire. Both antennas can be flexed as required to fit in different spaces.
The antenna does not need to be outside the nosecone provided that it is not made out of a conductive material. It is best to not fold the antenna back alongside the body of the tag though because that will reduce the efficiency of the antenna.
As far as the ruggedness goes, either model can easily withstand launch or typical landing accelerations. We have had some damage when the chute does not deploy and the rocket comes down at hundreds of miles an hour. The Ultralight model only has a heat shrink casing on it to keep the weight to a minimum (12 grams) so a direct impact to the body of the tag can cause damage to the circuit board or the battery. The Advanced tag has a waterproof and crush resistant polycarbonate case that is very impact resistant for all but the most violent landings. You can see a demonstration of that here:
