I had not heard of them before.  I did a quick internet search and looked at their website, as you have done.  They are headquartered in Montreal and have a "partnership" with Flipkey/Travel Advisor for discounted rates if the property is listed on both sites.  TRN does not appear to have very many listings.  They only have 99 listings for the entire country of Canada.  In the part of Maine where my property is located, they only have one listing (VRBO has hundreds for this same area).  I think that potential renters will be drawn to sites that have more listings.  Also, as you mentioned, Travel Rental Network seems to target travel agents.  Personally, I want to deal directly with the potential renter so that I can screen them myself.  Advertising 3 units for $349 for 16 months is not a bad price, however.  It might be worth taking out an ad for one year and see how many rentals it generates.