Yeah Billion phone support is very good, far better than more mainstream brands such as Netgear, Asus, Linksys et al.
Re: meaning of L2TP VPN, I'll try not to confuse you with technical mumbo jumbo and keep things simple
Think of L2TP (Layer 2 Tunnelling Protocol) as a method
of connecting to another network. However L2TP is just 1 method (protocol), there's a few others all with different degrees of security (encryption)
The well known ones are:
PPTP is the fastest but also the least secure of VPN connection methods. L2TP is better but again without suitable encryption. L2TP/IPsec is fully encrypted and is probably the best in terms of security versus speed. OpenVPN is the ultimate method when it comes to security but this comes at a cost: it is the slowest of all VPN protocols due to the large overheads it uses to secure the tunnels. OpenVPN isn't 100% secure (no VPN protocol is!) but it would take many, many, many years
to crack open an OpenVPN tunnel so realistically its bulletproof.
If you wanted to keep your browsing history away from the prying eyes of MI5/GCHQ then you would use OpenVPN preferably at router level to secure your browsing. Routers such as the Asus ROG GT-AC5300 or RT-AC86U are the ones highly recommended for running OpenVPN server/client. However setting up OpenVPN on a router isn't for the faint hearted!
Where security isn't that important (eg unblocking geo restricted websites or getting around CGNAT issues like in your case) then using a PPTP or L2TP VPN is the easiest/fastest method which is why AAISP offer this VPN method.
FluidOne FTTPoD 330/30