At the moment I haven't got a tempo trainer. My original model died when I left it switched on by accident and so far I have resisted the temptation to buy one of the new models, although the fact that the battery is replaceable makes it more attractive.
When I had the TT I could easily swim at tempos of 1.3 or so and tried tempos as quick as 0.9 but generally found that I didn't go any faster. As far as I remember my lowest normal SPL was at around 1.7, although I'm sure I tried tempos above 2.0.
A few years ago I could easily swim faster than 30 seconds for 25 meters from a push and my best time in a meet from a dive was 24.99. Now it is rare for me to go faster than 32 seconds from a push. I may have a chance to do a 25 meter race from a dive later in the year.
My best time for a LCM 50 is 57.41, which I swam last year. This year I failed to break the minute.
I had the impression from Charles that actually by trying to swim as slow as possible I might find parts of my stroke that need work. I am already aware of some of them. I know I can swim slower than 3 minutes for a 100 meters LC because I have done so in the later stages of a 1500. I guess I can probably swim even slower than that. I'm sure I could easily swim slower than 4 minutes per 100 swimming backstroke and could probably do so almost indefinitely if I didn't die of boredom or cold.