Use UTM to UTM RED technology to replace IpSec VPN tunnel ?

Hello all,

I'm new in Sophos UTM world, so I have what can be a real beginner question:

Is it a good idea to use RED technology to set-up a site-to-site tunnel between two UTM (sg-310 and sg-125) instead of setupping an IpSec VPN tunnel ?

I took a look here https://www.sophos.com/support/knowledgebase/120157.aspx and it seems to fulfill our requirements.

The particularity is the two UTM are located behind NAT Devices ( front firewall and router to traverse to reach internet).

Actually we tried to setup an IpSec VPN between the two UTM through NAT and experienced strange issue , the tunnel establishement went well but then, we had a lot "INVALID_MAJOR_VERSION" error message in the VPN debug console (like if the IKE version was different betwee the two UTM ?!?) and no trafic seemed to go throught the tunnel... so we gave up...

Now i'm wondering if using RED technology will simplify our life establishing the tunnel through NAT devices or if having NAT devices on both side can be an issue ?

Thanks in advance for your answers.

Best regards,