I am a big fan of Suma but there is little information on FlyerTalk so I can provide some outlines to newbie's.

Suma has the same award chart for all partner airlines (Delta as an example below)
https://www.aireuropa.com/us/en/aea/...nes/delta.html
The award chart shines with short haul (<600 miles) for 6,000 miles in Economy and 12,000 in Business. or Very Long Haul (>3,500) 48,000 in Economy 90,000 in Business.

You can book partner airline flights 364 days in advance which is very competitive if you want to snag some hard to get redemptions like KE Long Haul Biz.
None of the partners have fuel surcharges which can be a big difference over other programmes.

If you are looking for award space I recommend the Air France app (not website it's too glitchy) they have access to the same award space as Suma (for KLM/AF check Virgin Atlantic).

Now the cons were mentioned above.
No refunds; no changes; no exceptions (unless your flight gets cancelled)
You have to call in for your redemptions; I wouldn't worry about locations they have international numbers and Skype can call the US number for free.
You likely can't combine partners. Agents can search Origin to Destination and it's possible that some flights will show up with mixed carriers all priced as a connection.
If not you can feed them flights segment by segment and they can manually long sell the ticket but they will add the distance for each carrier together and price accordingly.