Heathrow Fast Track for arrivals

I fly from Singapore to LHR very regularly and have never done this - passport control is just egates, so there's not a lot of chance for delays unless they have a complete meltdown. Generally we either go straight through, or there's a queue of no more than a couple of minutes.

I find the best timesaver for me is priority on checked baggage (if you have airlines premium status or are flying business or suites class).
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As Simon noted, if you are traveling on an Austrailian passport, and in the UK for tourist purposes, you get to use the egates.

I enter the UK a few times a year and have never had more than a five minute wait once I get to them. The walk from your gate to immigration usually takes longer than the line at immigration for the egates.

Just don't forget to get your ETA ahead of time.

I have used Fast Track for security when leaving the airport but that came with my ticket. It does seem to go quicker.

You don't need it- since they introduced the e-gates several years ago (which as noted above you can use as an Australian citizen) it only takes a few minutes to go through passport control. Now if you were asking this question prior to the introduction of the gates, or if you were travelling on a passport not accepted by the e-gates (most passports for non OECD countries), then I might look into this service, tho never having used it myself I can't speak to what it actually involves.

Thanks all for your help. Much appreciated.

What is Heathrow Fast Track Arrivals Passport Control?
Fast Track Arrivals Passport Control gives you access to a dedicated lane at passport control, helping you reach the border more quickly after landing at Heathrow. It's especially useful if you aren't eligible to use the UK's eGates. ( from the FAQ section)
https://www.heathrow.com/at-the-airport/airport-services/fast-track

OP question has been essentially answered but thought for future inquiries having the source document/info available might be helpful.

An issue for using it for arrivals is the plane being on time, but there is a refund process
Fast Track Arrivals
If your flight is delayed or cancelled, you can amend your booking until 20:00 on the day before your booking date, subject to availability.
If you decide not to amend your booking and your Fast Track Arrivals booking hasn't been used, you can request a refund within 30 days of your cancelled flight by providing valid proof.
If your flight is delayed on the day you travel, we'll do our best to honour your booking. If this isn't possible, you can request a refund within 30 days by providing valid proof of the delay.