First of all I will admit to being totally biased as I have been a Flatcoat owner for many years.
At the turn of the 1900's flatties were the top picking up dog but were overtaken by labs who mature a lot faster and not being as smart (I said I was biased) were more easily trained. These days flatties are very popular in the dog show world (won Crufts in 2011) which means there is not a high percentage of working dogs within the breed anymore. There are still people out there doing there best to try and keep the working and show strains the same but I think that is a battle that is an uphill struggle.
They were bred as bird dogs but can be very good deer dogs with the right training. I currently have two with one being used both for birds and for deer although he is mainly a bird dog as I don't shoot a lot of deer therefore there is not a lot of opportunity for him to find lost ones.
There is nothing better than to see a flattie out working as they are very stylish and are intelligent in seeking out their quarry. I have never found them slow but there again they are not super fast.
Downside with Flatties these days is they are susceptible to cancer. I must admit to being lucky having only lost one to cancer at the age of 7 others have gone to over 12. Like other popular breeds I think this is due to the gene pool being reduced by a high percentage of breeding being done by dogs who win at the likes of Crufts etc.
At the end of the day you go for the dog you like ensuring you get one who has the best background for what you want then you put in the hours of training. Its a bit of lottery but you try and stack the odds in your favour.
Mulac