Solo, it depends on the day.
Not really a 'sight' to rate — it's a tool. A good driver-guide spares you the brutal gradients up to the castle and the Graça viewpoints and narrates as you go, which is genuinely valuable if stairs are the enemy. The honest catch: quality is a lottery, they're pricey by the hour, and locals (rightly) resent the swarms clogging Alfama's lanes. The way to de-risk it is to book a named, reviewed operator rather than hailing one off the rank — Eco Tuk Tours, for instance, runs electric tuks with vetted guides, which also takes the noise-and-fumes objection off the table. Treat it as accessible transport with commentary, not a headline experience.