Tacktick or Speedpuck

the speedpuck has its uses if you want speed, if you are tidal the GPS compass is not as useful as you might think. i have both and use them together to help calculate the tidal lift / header. on the new dinghy it will be just the tacktick that will be put on to start with as we can collect gps data for analysis after on my phone (not as accurate as speedpuck but good enough for testing settings).
In conclusion lol tacktick is the best first purchase....we did us to use an app and waterproof phone taped to the mast for speed 

I'm familiar with Tacktick, but not with others. But I've found tacktick a great instrument - if nothing else its nice to have a countdown easily viewable on the mast.
I've used it - I think! - to good effect, even inland. Mind you, that was on a large lake (Rutland) - on a small fgravel pit then really the shoreline ought to be close enough to give you a good point of reference up a single beat. Less so perhaps from one lap to the next.
But I agree with Cirrus about keeping eyes out. My first few outings of a season would be leaving it ashore - first off get yourself back in tune with the outside world. Technique and speed first, tactical niceties after!