I'm using Skinny 4G with the B618s modem. The cell tower is only 100 metres from me, so my reception is pretty stella.
I find it good. It is faster than ADSL2+ the majority of the time, but in peak times (from early to late evening and right through the weekend) it can sometimes be equivalent to and occasionally even lower than I would get with ADSL2+ due to network congestion. The best speeds I've managed on speedtest.net are 85mbps down and 45mbps up, but when it's congested I've gone as low as 2mbps down - not joking!! Fortunately this is very rare. Most of the time I get better speeds than ADSL2+, but not hugely.
I've not tried it, but a family member with Skinny 4G says he can't connect with a VPN when using wireless 4G, but he can on ADSL. He also said he notices a bit of latency and packet loss with 4G, which affects gaming. I'm not a gamer so this isn't an issue for me. Honestly if you have a decent VDSL connection, I'd stick with that, but like someone else said you can always try 4G and if it doesn't suit, must return the modem within 30 days.