Frankly, the less information you can put into this thing the more it's assuming you're someone else other than who you are. I would put more stock in online pages that let you configure your gender, weight, and also height.
If you don't have a reliable way to get a good calorie burn figure, then like Sky says, don't worry about it! Just get a good quality workout where you feel taxed by it and feel like you challenged yourself. That will definitely see improvements, no matter what the numbers are.
For tracking then, you just use the best estimate you can.
For cardio it will be a reasonably safe bet, but only for cardio. And as you said, the less information it allows you to program in the less accurate it will be. If yours won't allow gender, height, or activity level then it's going to be off by more than another person's model that DOES allow that information.
Thing is, HRMs are great if you are training for something or just now learning how to work out, getting your fitness level up. For fat loss, though, you really do not need it. What matters for fat loss is the QUALITY of your workout and calorie burn, not the QUANTITY.
The problem I see time and again (and am myself guilty) with heart rate monitors is that people get obsessed about the numbers they see on their screens and start to think that MORE is BETTER.
And that's just not the case.
Getting a quality workout, not a quantity workout, will serve you better for fat loss and health in general.
Not for beats per minute -- my hrm has a chest band and I know that part is accurate. HOWEVER, I'm wondering how accurate hrms are when measuring calories burned? I can put my weight in, but I can't put my gender in (I'm female) so I'm assuming it's going to be a bit on the high side either way (they usually assume you're male if you can't specify). People with heart rate monitors: how much stock do you put in the "calories burned" measurement on your heart rate monitor?