No definitely not. It's nice to have someone asking sensible honest questions here.
Normally it's "I broke my alarm help me fix it now for nothing"...anyway...
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Obviously 2 way wireless is better than 1 way but the cost will be greater, you will be able to see this from the costs in the quotes. It all depends on the risk of the property.
The main pro to the 2 way is the added security of knowing your signals have been received at the panel. Also faults will be displayed instantly whereas on a 1 way a fault may take several hours to appear depending on polling times etc.
I think our resident JW put it best...
If something important gets lost in the post you'll wish you had sent it recorded.
Also not included in your OP is 2 way wireless mesh like the Texecom Ricochet range. This "mesh" means the sensors can talk to each other not just the panel. However, in smaller houses you could there is no benefit to this.
Other pros are 2 way can benefit from greater battery life due to the panel being able to put sensors to sleep while disarmed and switch LED's on and off remotely. Not all 2 way panels will do this but it's possible so bear it in mind.
The kit should be equally as reliable from a parts going faulty POV, some alarm companies prefer certain manufacturers over others. Personally I'd look at the Texecom 12-W, for example.
As for size of the devices that's personal preference, have you not had a company round with a demo kit to see the devices in the flesh? I would want to see the property before quoting to assess the risk, it's ok to give an estimate over the phone but you could be over looking something.
Very sensible.