Both do the same basic job: they close an opening after hours so that glass is not the only thing between the street and your stock. Beyond that they behave very differently, and the right choice depends on the building, the street, the planning position and what you want passers-by to see at night.
Roller shutters
A roller shutter is a curtain of interlocking laths that coils into a box above the opening and runs in guide rails at each side. Curtains come in several types. A solid steel or aluminium curtain hides the frontage completely and takes the most punishment. A perforated or punched curtain lets light and some visibility through. A tube-and-link or brick-bond curtain is an open grille that rolls, so the window stays on show while the shutter is down. Polycarbonate curtains give full visibility with less strength.
Shutters can be manual, with a pole, crank or chain, or electric with a key switch, remote or link to the alarm. Electric is the norm for anything above a small shop door. They need headroom for the box and a flat fixing surface each side for the guides, which arches and uneven stone fronts do not always offer without a sub-frame.
Collapsible grilles
A collapsible, or concertina, grille is a lattice of steel bars and rivets that folds sideways into a stack when open and is drawn across a top track when closed. It is nearly always fitted inside the glass, so it does not change the look of the building from outside and the window display stays visible at night. It needs no headroom, which is why it suits arches, low fascias and listed frontages, and it can follow odd-shaped openings that a shutter cannot.
The trade-off is strength and effort. A grille will deter and delay, but a solid shutter resists more. A grille is also drawn by hand, so a wide frontage means several sections and a routine of locking each one. Floor tracks, where used, collect dirt and need keeping clear.
Planning permission and the street
External roller shutters change the appearance of a building, and in most places fitting one to a shopfront needs planning permission. Many London boroughs discourage solid external shutters on shopping streets and will not approve them in conservation areas. Open grille shutters, shutters fitted behind the glass, and internal collapsible grilles are far more likely to be acceptable. Check with the local planning authority before ordering anything, and ask your landlord if you lease the unit.
Insurance and security ratings
Insurers may set conditions for after-hours protection of a shop, particularly for high-value stock. Ask what they require before you choose. Some products carry a Loss Prevention Standard rating, LPS 1175, which grades resistance to attack. It is not needed for every shop, but it is a useful question to put to a supplier when stock is valuable.
Fire exits and escape
Whatever you fit, an escape route must stay usable from inside while people are in the building. A grille padlocked across a fire exit is a common and serious mistake. Where a shutter covers an exit, the controls or a release must work from inside without a key, and the arrangement should be agreed with whoever did the fire risk assessment.
Looking after it
Shutters and grilles fail at the worst moments, usually on a Saturday night. A yearly service that checks the curtain, the motor, the brake, the guides, the locks and the safety devices catches most problems first. Electric shutters that people can walk under also need their safety edges and stops checked, in the same way as an industrial door.
Choosing
For a conservation area, an arch, a low fascia or a shop that wants its window seen at night, start with a collapsible grille or an open-link shutter. For a vulnerable frontage where appearance matters less, a solid or perforated shutter gives the most protection. Many shops settle on a punched curtain as a middle way. Measure, check planning, ask the insurer, then decide.