Trittons are good, but I would definitely pay an extra £40 and get the Astros for the little extras. Astro A40s have more customisation such as being able to choose which side you keep your microphone on, or remove it all together if you just want to listen to music. It also has removable 'tags' on the ear cups where you can insert pieces of foam that come with the headset, these give you the option of blocking out sound better or leave the foam out to hear your friends around you whilst you play.
The mix amp for the A40 has a handy slot for connecting your MP3 player directly into it, so you can enjoy your music through the mix amp whilst being able to adjust the contrast between music and game sounds to find that perfect balance. The Tritton AX Pro aesthetically looks good but not sure about how comfortable it may be, where as I've always been telling people how surprisingly comfortable my A40 headset is compared to my TBX1 and SteelSeries Neckband.
So yeah, I would pay the difference in price because Astros are considered the peak for competitive console gamers, and they go the extra mile with their products. However it's worth noting that my experience with Tritton's AX Pro was very brief, which is why I focused on the features the A40 offers that isn't available on the AX Pro from what I can tell.
I will pick up the AX Pro at some point and review it.
