After having test some receiver, naturally, I’ve tested some transmitters, the objective is the same : get the best coverage in the same condition : I would say poor conditions. Lots of wires going every where and an antenna make with a simple 17.3cm wire. As expected, results vary regarding the emitter used. Reed more to get details.
The test is made by emitting a signal in 2 sequences of 4 messages sent. I move a receiver over different area of my house. Some are same floor, some are one floor below and some are underground. Distance is from 2 meters to 15 meters. Different wall thin or large are on the way. I won’t detail, it is not the objective. We will name room A,B,C,D,E,F,G,H. Result will be OK when received 2 sequences have been received. KO otherwise.
The first one is a really low cost emitter / receiver kit you can found here for 3.76€ HT. It is operated with 5V VCC and 3.3V GPIO – The result is :
A : OK | B : KO | C : KO | D : KO | E : OK | F : OK | G : OK | H : OK
Score is 62%
The second module 
can be found here for 6€. It is operated at 5V Vcc with a GPIO working at 3.3V.
The result is :
A : OK | B : KO | C : OK | D : OK | E : OK | F : OK | G : OK | H : OK
Score is 87%
The last module tested can be found here for the price of 5.5€. It is operated at 3.3V as for Vcc and GPIO. The result obtain from this component is incredible !
The result is :
A : OK | B : OK | C : OK | D : OK | E : OK | F : OK | G : OK | H : OK
Score is 100%
Have you tried this one TRM-433-LT ?
It’s a transceiver with a triggering pin (that can be linked to a GPIO pin).
The datasheet shows a -112 dbm sensitivity in receiving mode as for the QAM -RX1 that you have tested.
Oh, it’s also a 3.3 V input device…
No, I have not, the reason is that this product is twice expensive as the one retained so for my project i did not expect a better result for a such difference. But i use the transmiter from this brand and they have really good products.
That’s OK. You are right: the result would not have been better.
It might give other opportunities for home automation for instance: but it’s another topic 😉