I plan to do a sparkler send off and have a few questions! (Yes it’s allowed with my venue

what is the cheapest site to purchase from? (The real wedding sparkler type!)
what are the pros and cons of purchasing ‘real wedding sparklers’ vs higher quality ones from Walmart?
What size sparkler do you recommend? How long did what size you got last?
How long did your entire send off last/how many guests were present?
Im expecting 50-60 people at most and am not sure if everyone will stay for the send off!!