Sprint tri in 68-70 degree water.

I wouldn't.  As said, it is most definitely not a safety device, not really even 'safer'.  Do not think of it that way.  If you get into any kind of trouble in the water, it will not save you.  Not even a little bit.

It will likely enable you to swim a tiny bit faster, time that you are very likely to give back (in a sprint), quite possibly with change, while you attempt, for the first time in a race, to remove the thing.

Swimming in a wet suit isn't much different from swimming without a wetsuit.  If you are a strong swimmer you will be able to complete the swim with or without a wet suit.  If you are weak swimmer you will struggle with or without a wet suit.  The advantage of a wet suits is speed.  The weaker a swimmer you are the more time in the water a wetsuit will save you.  Strong swimmers will have good form with their hips high in the water whether they have a wet suit or not.  Weak swimmer will benifit from the boyancy because it will aid at keeping hips high in the water and the improved position with will reduce their drag through the water.  This mean you go faster, but it also means that you won't have to work as hard to move through the water so you will be fresher coming out of the water.  Wet suits also have slick finishesh, grip panels, etc. to move you through the water faster. 

The only problems I have had with wet suits are:

1) Leg Cramps : I don't know if the wet suit caused these but think it was a factor due to the compression on the legs.  I have got cramps 50% of the time I have swam in a wet suit and only about 1% of the time when I have swam without a wet suit.   

2) Shoulder restriction:  My first wet suit was probably too small for me (which put extra compression of the legs to cramp) and pulling my arms through the water felt like pulling elastic medicine bands.  I was 15 sec/100m faster so I was okay with that but it felt like I was shortening my stroke.  

3) The Kick:  I think my 2nd wet suit had the maximum allowable buoyancy in the legs.  I couldn't get my legs to go down in the water to kick.  They just floated on the surface(this reduced leg cramping because I didn't do as much kicking but I still had to kick some for balance in the water).

It would be good to swim at least once in the wet suit before the race to know how it feels in the water and what you can and can't do in it.  Once in the water is enough before race though.  You should be faster and save energy in the water (which in turn makes things safer).  You also should be able to float on you back really well in a wetsuit (this also makes you safer).