Bosch GEX 18V-125 Random Orbital Sander Review UK

Overview and first impressions

The Bosch GEX 18V-125 is the cordless random orbital sander from the Bosch 18V Professional range – the blue-label trade line rather than the green-label DIY products. It is sold body-only and assumes existing 18V Professional battery ownership, slotting into the same platform as the GSB 18V combi drills, GDX impact drivers and GWS angle grinders that many trade users already run. At around £90 for the body, it sits at the premium end of the cordless sander market for this voltage class, and the question the review needs to answer is whether the performance justifies that price compared to both lower-cost cordless options and the corded alternatives available for considerably less.

Build quality is immediately the stand-out characteristic. The GEX 18V-125 has a genuinely premium feel to it – the housing is robust without being heavy, the grip surfaces are well textured and the overall fit and finish is noticeably better than similarly priced tools from some competitors. Bosch has included a feature they call Constant Electronic, which maintains motor speed under varying load conditions rather than allowing speed to drop when the disc meets resistance. This matters in practice because consistent orbital speed is what prevents swirl marks and produces even results across a surface.

Specifications and test results

Performance and limitations

The Constant Electronic speed control is the GEX 18V-125’s defining practical feature. On test, it maintains orbital speed noticeably better than non-regulated cordless sanders when pressure is applied to the pad – the motor compensates for the additional load rather than dropping speed and risking swirl marking. This is genuinely useful during prep work where sanding pressure varies naturally as you work across a surface, and it produces more consistent finish quality across a single sanding pass than unregulated motors typically achieve at this voltage.

The 2.5mm orbit is the smallest of the sanders in this review batch. In practice the difference between 2.5mm and 3mm is marginal for finish quality at 180-grit and above, but the smaller orbit does limit stock removal speed compared to 3mm alternatives. The 80-grit test on pine rated only Good rather than Excellent for this reason – material comes off more slowly than on the Makita DBO180Z or DeWalt DWE6423. For users whose primary use is finishing and preparation rather than heavy removal, the 2.5mm orbit is entirely adequate and the speed regulation advantage more than compensates. For users who need to balance heavy removal with fine finishing, a slightly larger orbit would be preferable.

Runtime on a 4.0Ah battery reached approximately 35 minutes of continuous sanding under typical working pressure, which is adequate for most single-session jobs. A 5.0Ah battery extends this to around 45 minutes and is the recommended configuration for anyone using this tool for extended site work where stopping to swap batteries mid-task is disruptive. The compact 2.0Ah battery reduces tool weight noticeably and is worth considering for light finishing passes where runtime is less of a concern than balance. The tool accepts the full range of Bosch 18V Professional batteries and works well with both the compact 2.0Ah and the larger 5.0Ah options depending on the balance and runtime priorities of the task. The dust bag supplied performs comparably to other manufacturers at this level – useful for light work but benefiting from a vacuum connection for extended sessions. The dual-port dust extraction accepts both 27mm and 35mm hose diameters, which increases compatibility with workshop extractors compared to single-port designs.

Final verdict – is it worth it?

The Bosch GEX 18V-125 is a well-engineered cordless sander that earns its premium build quality reputation. The Constant Electronic speed regulation is a genuine differentiator – it produces more consistent finish results than unregulated alternatives when working at varying pressure across a surface, and for users whose work demands reliable quality on hardwood and painted surfaces, that consistency matters. The 2.5mm orbit and the higher body-only price compared to the Makita DBO180Z mean it scores slightly lower on overall value, but the build quality and speed regulation give it a distinct advantage for precision finishing work.

For existing Bosch 18V Professional users, the decision is straightforward – the GEX 18V-125 is the obvious platform sander and the quality justifies the price within the battery ecosystem. For those entering the cordless sander market without existing platform loyalty, the value calculation is harder: the Makita DBO180Z offers a 3mm orbit and comparable performance at a lower body price, while the corded DeWalt DWE6423 delivers excellent results for less total investment with no battery requirement at all.

The GEX 18V-125 is not the strongest performer in this group on raw sanding speed, and it is not the best value for a platform newcomer. It is, however, the best-built of the cordless options reviewed and the most consistent on finish quality at medium to fine grits – which is exactly what a professional decorator or furniture maker needs from a job-site sander. If that profile fits and you are already on Bosch 18V Professional, it is a confident recommendation.

Recommended Bosch 18V Professional batteries for the GEX 18V-125