>We don't really care about what they do or how they do it. What we care about is how do we approach the market. We have'nt really started yet. Our app is tested by businesses in that market but besides that nothing more.
>
>We're still establishing the right way to approach potential customers. We thought we'd have more time to do it but now it seems that we'll be forced to act faster. Because of the characteristic I mentioned.
>
>So I guess the big question should be : Should we start with marketing right away? Even if the product is not finished (but should be soon).

Yes attack them with ready application as fast as possible.
Offer low cost upgrade from their apps to your.
Offer easy data transfer from their apps to your. Most of customers refuse to switch if they couldn't transfer data archives
And if you get one of their biger customers market this as loudly as posible
I wish you sucsess.