2 x 300w RMS bridged is pretty decent for £120.
Most car speakers 90%+ are 4 ohms (it will be printed on the back of your car speakers) so you really only need to take notice of the 4 ohm rating of this amp.
You can run certain speakers at 2ohm instead of 4. Doing this will increase the output of the amplifier.
I'm not sure you can stack fuses together like that. Its 30A per 2 channels. ie ~430W peak per side. You can see on the stats that 2 channel is around 300W RMS and fuse blows at around 430W peak +- environmental/manufacturing factors which could be another 10-15%.
i followed some of that up to: "run into a 2ohm load." Could you ELI5 the significance of that?