Several times faster on open flat ground, and the finish is better - which is usually the more valuable half.

A lance cleans a narrow band and requires disciplined overlapping to avoid stripes. A surface cleaner sweeps its full working width in one steady pass, and the rotating bar guarantees the overlap for you.

The gain grows with area. On a small patio the setup time may not be repaid; on a forecourt, warehouse floor or car park the difference is the difference between one day and three.

Finish quality is where the argument is usually won. Striping on a large cleaned area is highly visible and effectively impossible to correct without redoing the whole surface.

Fatigue counts too. Pushing a surface cleaner for a day is far less tiring than holding a lance against its reaction force, and tired operators produce uneven work.

Match its rated flow and pressure window to the machine's actual output - the bar has to spin at the designed speed to clean evenly.

Every attachment states a flow and pressure range. Below the range the bar turns too slowly, the jets dwell, and the result is a spiral pattern on the surface. Above it, the bar over-speeds, cleaning efficiency drops and bearings and seals wear rapidly.

Flow is the dominant term. A machine with high pressure and low flow often cannot drive a large surface cleaner properly, and the fix is a narrower unit rather than more pressure.

Working width follows from available flow. A wider unit needs proportionally more water to keep the same cleaning intensity, so specifying a wide head on a modest machine is self-defeating.

Check the nozzles fitted. Many units allow the nozzles to be changed to re-tune the attachment to a particular machine.

The widest the machine can properly drive and the access allows - restricted by doorways, gates, aisles and how the unit is transported.

Wider covers more ground per pass, but only if the machine can supply it. An underpowered wide head is slower in practice than a well-matched narrow one because the operator has to go over ground twice.

Access sets a hard ceiling. A head that will not fit through the gate, between racking or into a lift is useless regardless of its performance.

Narrow heads suit steps, walkways, small yards, between-vehicle work and anywhere with obstacles. Many operators carry two widths for this reason.

Edge performance matters more than width for some work. Units with a brush skirt that can be lifted, or with an offset design, clean closer to a wall - otherwise every job still needs a lance pass around the perimeter.

On sound concrete, tarmac, stone, block paving and industrial flooring, yes. On soft, loose, jointed or delicate surfaces, with care or not at all.

Hard, flat, sound surfaces are what these are designed for and where they excel.

Block paving and jointed surfaces need judgement: the jets will strip jointing sand and it must be replaced afterwards, which is a known part of the job rather than a surprise. Weak mortar joints can be washed out entirely.

Timber decking can be cleaned with a suitable low-pressure unit, but the standard attachment on a powerful machine will raise the grain and damage soft boards.

Uneven surfaces defeat the design. The shroud rides on the high points and the standoff varies, which produces exactly the uneven cleaning the tool exists to prevent.

Test in a corner before committing to a large area - the tool's speed means a mistake covers a lot of ground quickly.

Nozzles, the rotary swivel or bearing, the skirt and the castors - and worn nozzles are the usual cause of a unit that has 'stopped working properly'.

Nozzles erode. As the orifice widens the pressure drops and the spray pattern degrades, and because it happens slowly the operator adapts without noticing. Replacing nozzles as a set on a schedule restores performance dramatically.

The swivel carries the water into the rotating bar and is the other consumable. A leaking or stiff swivel shows as poor rotation, dribbling from the top, or a unit that will not spin at all.

The skirt keeps spray contained and wears against the ground. A ragged skirt sprays the surroundings, which is one of the main reasons the tool was chosen.

Castors and wheels seize with grit. Cleaning and lubricating them takes minutes and stops the unit dragging and scratching the surface.

Some units can be used vertically, but most are designed to be pushed on the floor and handle badly on anything else.

The design assumes gravity holds the shroud against the surface with the operator pushing. Held against a wall, the whole weight and the reaction have to be supported by the operator, which is tiring within minutes.

Lighter units and purpose-designed wall or vehicle attachments exist for exactly this, usually smaller in diameter and with handles arranged for the position.

Overhead work with a surface cleaner is generally a bad idea. Water and debris return directly to the operator, and the tool cannot be controlled reliably above shoulder height.

For walls and high surfaces, telescopic lances with a suitable nozzle are the correct tool, with the operator standing back rather than under the work.

Yes - edges, corners, vertical faces, steps and anything not flat still need one, and chemical is usually applied with a lance too.

No surface cleaner reaches fully into a corner or right up to a wall on every side. A perimeter pass with a lance is part of the method, not a failure of the attachment.

Steps, kerbs, drainage channels, plinths and street furniture are all lance work.

Pre-treatment is usually applied through a low-pressure or foam nozzle on a lance, allowed to dwell, then removed with the surface cleaner. That sequence handles soils a surface cleaner alone will not shift.

Practically, the two tools swap on the same quick-release coupling, so the change takes seconds and both stay on the job.