running the QT backtest for 3x UIS with rebalancing every two weeks, the 10yrs performance drops slightly (3% p.a.), but this is considering also rebalancing SPXL every two weeks. Not an easy way to backtest changing only TMF, would guess it´s slightly better, or less of a drop.
From a practical perspective I would also opt to rebalance TMF every two weeks. See screenshots attached.