The Draytek modems are superb if you have a short line, the 130 was disappointing sync speed performer on my ultra-long BTW ADSL2+ line.
They protocol-convert between PPPoE over Ethernet on the LAN and PPPoA over DSL. PPPoA over DSL is of course more efficient than PPPoEoA over DSL (around ~3% faster with 1500 byte IP packets, if my maths is up to it). Could be zero difference with certain packet lengths, could be 50% worse with certain very short packets.
But that's all as nought if the Draytek doesn't sync as fast as alternative modem X.
Does Sky ADSL (presumably ADSL2+?) allow PPPoA?
One other nice thing about them is that they allow you to have full 1500 byte MTU (IP total PDU length) rather than 1492, so no chance of any MTU problems on the internet, but this is only achievable if your router can handle exchanging ‘baby jumbo’ Ethernet frames with 1508 byte payload with the modem, containing PPP + PPPoE. If not, you're stuck with reduced MTU. Another nice thing about the Draytek 130 is it’s zero config, it just works, on BTW anyway, wouldn't know about Sky.
I use three DLink DSL-320B-Z1 PPPoEoA-over-DSL modems on my 21CN ADSL2 line. So much faster sync rate on my ultra-long-line that the 3% performance loss compared with the Draytek on big up-/downloads due to PPPoEoA inefficiency is irrelevant. Ultra-cheap compared with the Draytek, and like the Draytek supports full 1500 byte MTU (but not possible on 20CN because of BTW) with the same conditions on the router’s PPP + PPPoE 1508 support. If you decide to try a DLink it's vital to read health warnings about safe and sane config in earlier thread. (Scary security holes, bugs and insane DSL settings if used with default config, but extremely easy to fix.) Otherwise they're zero-config, on BTW anyway.