The signage from Terminal 3 at YYZ is poor. You have to take the (free) SkyTrain (or whatever it's called) from T3 to T1.
As mentioned already, there are two downsides to the service right now....it's expensive and connecting to the TTC at Union Station is arduous at best. Also as mentioned before, the signage has improved. But I just can't see sane-minded people, traveling on business or pleasure with a lot of baggage wanting to take this service.
They got greedy with original fares. Note that as of March 9th, they're dropping the fares to $12 without Presto Card, $9 with Card (until then $27.50 without card, $19 with). Ask for the free voucher if you're paying before March 9th (they make the announcement in the train, but you have to ask for the voucher).
Once they somehow streamline this with TTC (subway) at Union Station, this is going to struggle to be profitable.
On the good side, cars are new, clean have wi-fi and AC power.