The CD250 shares the same Band 20+3 dual bands and ≥60/≥65 dB gain but outputs ≥17 dBm and covers up to 250 m² for 25 users; the CD500 keeps the same gain but raises output to ≥20 dBm (≈100 mW, about double) and reaches 500 m² for 50 users. The C500 is a single Band 20 (800 MHz) unit that boosts O2/Vodafone 4G over 500 m² but misses EE Band 3 4G and voice. Choose the CD500 for a large home, office, farm or warehouse where 500 m² and 50 users with both bands matter; step down to the CD250 for 250 m², and choose the C500 only if you are O2/Vodafone-only and do not need EE.

Band 20 (800 MHz) is the rural propagation band used by O2 and Vodafone for 4G, reaching further over distance and through obstacles; Three 4G rides Band 20 over the shared O2 MOCN. Band 3 (1800 MHz) carries EE 4G alongside the EE 2G GSM layer for calls and SMS. The CD500 amplifies both simultaneously, so an O2 phone and an EE phone in the same large premises both get boosted 4G without switching boxes.

Up to 500 m² (5,382 ft²) means a detached or extended family home, a large open-plan loft, an office floor, a farm house/cottage, a café/pub or a single-storey warehouse. It is not a whole-estate, multi-storey mansion or full commercial warehouse solution; beyond 500 m² a distributed multi-antenna system is needed. Solid stone walls, metal cladding and distance from the whip shrink the usable area.

The CD500 supports up to 50 phones or data devices connected at the same time, sharing the boosted Band 20 and Band 3 capacity. This suits a team office, a large family home with guests, or a busy café/pub floor. Beyond 50 active users the shared RF capacity thins out; a large open-plan company office or full warehouse needs a higher-capacity distributed system. It is connected capacity, not a guaranteed 50 fast-speed lines at once.

Gain in dB measures how much the amplifier strengthens the signal: ≥60 dB uplink lifts your phone's signal back up to the mast, and ≥65 dB downlink lifts the mast's signal down to your phone. Output in dBm measures the final radiated strength: ≥20 dBm is about 100 mW, roughly double the CD250's ≥17 dBm (≈50 mW), and that higher radiated power is what reaches across 500 m². Gain and output work together — high gain without enough output still leaves far corners weak.

The CD500's flagship ≥20 dBm output is the hardware difference that covers a larger 500 m² space; all three share the same ≥60/≥65 dB gain, so the extra coverage comes from radiated power, not more amplification. Each +3 dBm roughly doubles power: ≥10 dBm suits 200 m², ≥17 dBm suits 250 m², and ≥20 dBm reaches 500 m². The unit remains in the Ofcom licence-exempt mobile repeater class; it is not a licensed high-power outdoor transmitter.

The supplied 5 dBi omni works well when you have a clear, unobstructed mounting spot with 1–2 bars outside and do not need to aim at a specific mast. Where donor signal is very weak, or the mast lies in one direction behind a ridge or trees, a high-gain directional focus on that mast often makes the difference between marginal and solid; the kit already includes the donor aerial, so start with the omni, read the bar count, and add directional focus only if signal stays weak.

At least 1–2 bars of usable outdoor signal on Band 20 and/or Band 3 at the omni mounting point, checked with a phone outside on the wall, roof or eave. A booster amplifies the donor signal it receives; it cannot create signal where none exists outside. If your phone shows zero bars and emergency calls only even at the mounting point, this unit will not work, and neither will any Ofcom-legal booster at this price.

The CD500 carries a 365-day money-back guarantee: if it does not work for your location, return it by mail within 365 days for a refund; return shipping is deducted from the refund (ReturnShippingFees), so it is not a free-return label. Standard delivery is free: handling takes 1–2 working days and UK transit 10–15 working days, so it is not next-day, and the same policy covers 15 European countries (GB, DE, FR, IT, ES, NL, BE, AT, SE, DK, FI, IE, PT, PL, CZ).

The CD500 boosts 4G LTE data and 2G calls/SMS; calls over 4G work when your handset and network offer VoLTE (Voice over LTE), which O2, Vodafone, EE and Three support on compatible plans. It does not boost 5G NR on any band and it does not boost 3G UMTS Band 1 (2100 MHz), so a device stuck on 3G fallback will not be helped. If 5G speed or 3G fallback is the main requirement, a different unit on those bands is needed.