So what hardware are we recommending these days for load-balancing? I'd be interested in shifting traffic onto 4G when my ADSL2+ is saturated

Also following with interest, again looking at mixing ADSLmax with mobile data. Have been looking at TP-LINK TL-470T+, which does a good job on QOS to balance out users on slow ADSL, can also see if use THREE, how to redirect Netflix traffic over mobile to use go binge. The issue I can't see is how to boost general use without exceeding data limit.

I can't really make a considered recommendation as I only have experience of one router - a Draytek Vigor 2860n+. That has a whole load of features that allow various load-balancing and routing configurations. Not all are easy to set up or even understand. It does allow ADSL/VDSL to be load balanced with ethernet connections (e.g. from another router) or using WiFi to tether to a hotspot (e.g. a MiFi, phone or 4G router) or using a 3G/4G dongle (they list the ones that are supported/tested).
It can disable a WAN when it reaches a monthly data limit (useful with 4G). You can force certain traffic through a particular WAN (e.g. you could use 4G for Netflix).
Another option is to use failover, where a WAN is only used when another fails or reaches a set traffic level - that can reduce the traffic on a 4G connection to just the times you need the extra bandwidth.
I'm sure there are other routers that offer the same sort of things. I would recommend getting one that can tether though - allowing your home network to share your phone connection could be useful as a fallback when your ADSL/VDSL is out of action.

Good point: using a tethered connection would be very useful. thanks!

Beware that "binge" style offers tend to be a degraded quality, for example, capped at 480p. Arguably fine on a phone screen, but disappointing on a 55-inch telly

Slightly off topic, but when speedtests and TBB Map stats occur on bonded lines, do they show an effective single line speed?

Just imagining how others using the map might pull their hair out, seeing double their speeds in their area, if it shows the bonded speed.

I too am using a Draytek (2925) to load balance an ADSL connection with a FIXED WIRELESS connection. Well it used to be for load balance, now it is primarily for fail over as we use the FIXED WIRELESS for pretty much everything but the Draytek has been reliable and offers some quite advanced functionality albeit nothing like as flexible and powerful as a Mikrotik which will let you load balance as many connections as there are ports on the router, a feature which a lot of the more advanced routers support (steep learning curve if you are not familiar or from a tech background).

In reply to a post by richi:

Beware that "binge" style offers tend to be a degraded quality, for example, capped at 480p. Arguably fine on a phone screen, but disappointing on a 55-inch telly

Not any more after recent Ofcom Rulings - both Vodafone (passes) and Three (Go Binge) will operate at full resolution

In reply to a post by camieabz:

Slightly off topic, but when speedtests and TBB Map stats occur on bonded lines, do they show an effective single line speed?

Just imagining how others using the map might pull their hair out, seeing double their speeds in their area, if it shows the bonded speed.

Generally a speedtest on a bonded service will appear from the geolocation of the data centre hosting the aggregation side... that said on a TBB test by postcode, yes it would show up as a faster speed, but with either an unknown ISP or a lesser known provider if they feature in TBB ISP listings.

That's good news. However, I bet those streams are still deprioritised, so when the cell is congested the streaming service itself will automatically switch to a stream that's lower bitrate, lower resolution.