Update:
I found that the Taoglas TG.30.81131 gave me a benefit of about 3-5dB RSSI as measured with Cellular.RSSI over a period of about 16 hours. The max/min distribution scaled consistently, no change there.
None of the other antennas (except for the other varients of that same Taoglas one) gave any significant improvement.
For me, that wasn’t significant enough to warrant the extra cost in certification hassle for the time being, so I’ll be sticking with the stock antenna.
If you need a flexible antenna for some reason, the Antenova seemed to work ok, though slightly underperformed the stock Taoglas.