Hi,
we've flown from Ogdensburg twice this year (and are flying from there again at Easter) and are very happy with having the service. Before that, we've flown over a dozen other times with AllegiantAir (from Plattsburgh, Syracuse, Elmira and Scranton (we might have gone from Allentown once)). We've had a couple of delays although I think only 1 time it was significant (about 3-4 hours), another time the plane had to take off from Syracuse, land in Pennsylvania, refuel and then go to Florida which was very odd but they had told us before bording that it would be happening (It was one of Allegiant's first flights from Syracuse (maybe the first one) and my guess is that they had not yet received credit approval to refuel there so had to go to another airport ...) and at XMas, our landing in OGS was aborted and we had to land in Plattsburgh because there was too much ice on the runway at OGS - a couple of hours later we landed in OGS. But we've never had a cancellation.
For us, the biggest attraction is the price and direct flights (we'd much rather have a flight delayed or even cancelled at home than get stranded in airport in the middle of nowhere overnight because the connection was cancelled). As mentioned above, AllegiantAir does nickle and dime for pretty much everything (luggage, seat selection, meal, etc) but I don't think it's that different than other airlines. If you only take the economy fair, I think pretty much all airlines charge for luggage now (although maybe not for carry-on which Allegiant does - we pretty much always only travel with our "personal item" (luggage under the seat in front of us so don't usually pay any extra). They charge for seat selection but I don't think we've ever paid for it (we're pretty much always close by and I believe they told us that by law, they can't sit a young child alone so one adult always seats next to each child). They also charge for priority boarding which I'd never pay for (the last thing I want to do is sit even longer in the airplane and we always board at last call. Parking is no longer free in OGS but I believe it's still quite a bit cheaper than in Ottawa (there's a nearby garage that offers parking for half the price but I haven't used it yet). You also have to pay the toll on the bridge in both directions. Another attraction is that we'd much rather cross the boarder by car than going through customs at the airport.
We live in the East End of Ottawa and because crossing the boarder by car is much faster than going through airport security, I think we can leave for flight from Ogdensburg at roughly the same time as we'd leave for a flight from Ottawa. I'm guessing that for someone in Barrhaven or Kanata, it's faster to go to Ogdensburg.
For 2 people, if you can get a reasonable price from Ottawa, I can see that it might not be worth the hassle to go to Ogdensburg (although I don't really see it as a hassle). We're a family of 4 and the savings add up quickly.
Someone mentioned flying to SFB vs MCO which I admit is not ideal (no DME, I believe rental cars are more expensive at SFB (harder to get deals) but I much prefer SFB. We flew from MCO-YOW a few years ago at XMas time and it literally took me 2.5 hours to get through security at MCO. They were holding the plane at the gate for me and were paging me by the time I made it to the gate ...
As far as other airlines flying from Ogdensburg, I suspect that it's not likely to happen for a long while. First the airport is tiny and I don't think they can even handle more than 1 flight per day (I'm not counting CapeAir which only flies a small Cessna), secondly Allegiant subsidized the airport expansion so I wouldn't be surprised if there are some non-compete clauses for a while and finally, I really don't think it will happen until there's a lot more Allegiant traffic at OGS.
As far as other nearby US airports, we pretty much only travel in the winter so I'd be hesistant to drive to Rochester or Buffalo and would consider Plattsburgh, Syracuse, Elmira and Scranton before (Scranton is the same distance as Buffalo but at least it's in the right direction! And I'm kind of paranoid about getting lake-affect storms so prefer staying on the 81 versus driving on the 90)
Back to the OP's question. Unfortunately, looking at the schedule, I suspect the reason you can't buy tickets for OGS-SFB flights in August is because Allegiant Air isn't offering OGS flights from mid-August to October (they do this quite a bit in seasons when demand is lower) ... I would check with them and confirm that this is the case and if it is, tell them that if they do add a later August flight, you'd likely take it. Many schools in the US start mid-August so tourism reduces at that time of year and they are probably setting their schedule according to that. I suspect that if they get enough demand, they would add flights (I've seen them add flights around XMas time).
Hope this helps,
Mike