How is a 25%+ drop in power "satisfactory"? That's a huge loss, leading to a significant increase in the sample size / test duration required to reach the same level of significance. A comparison with other sequential methods reveals Always Valid p-values to have the worst performance even under favorable conditions: https://blog.analytics-toolkit.com/2022/comparison-of-the-statistical-power-of-sequential-tests/ and hence the worst trade-off between average sample size and power.